The validity of a marriage is determined by the society's belief that the permanent sexual union of two legally competent partners creates a new line of socially beneficial kinship. This cannot be established by political fiat alone. It is based on nature and tradition, by which I mean congruence with the natural and customary extension of society.
Our society's recognition of those actions that form permanent kinship by extending and morally interlocking existing families is rooted in human biology and history. If we heard a government minister claim that permanent kinship would now be predicated upon a kiss, or a hug, it would not change the social understanding of kinship: that kinship is inextricably linked to the history of human survival.
As a minimum, our kinship system is geared towards society recognising and investing in human survival. This is the cause of marriage, the development of a new line of permanent kinship geared towards human survival. In contrast, the motives of those getting married can and do differ.
Motive and cause in marriage law.
Motive and cause have different contractual meanings. Gay couples can lay claim to the same loving motives for marriage as a heterosexual couples. Nevertheless, by constitution, the relationship opposes the cause of marriage, i.e. the chief reason which society uses to determine that the promises of marriage should be permanent and legally enforceable (what society recognises that those who marry must agree to). The reason is not to enforce love. It can't, so love is not the legal cause of marriage. However, it can ensure that those who claim its support and validation as marriage cannot abdicate their responsibility to their spouse, offspring and extended family without cost.
Marriage laws enforce commitment to support all legitimate outcomes of the marriage jointly. It imposes a cost upon anyone who marries and then abandons that kinship arrangement.
Marriage imposes a perpetual legal obligation that is predicated upon the outcomes of permanent exclusive union. Both forms of kinship (by marriage and by descent) are so closely related (cf. inheritance and incest laws) that they need to be congruent with each other. For example, close relation marriage is banned because it is incongruent with and opposes genetic diversity.
For our society to thrive, genetic diversity ensures that there is sufficient 'variation to ensure that some individuals in a population will possess variations of alleles that are suited for the environment'. The counter-argument that the world is already overpopulated cuts no ice. If a society does not maintain genetic variation, it can't survive upheaval and sudden environmental and habitat changes.
Homosexual relations are incongruent by constitution with genetic diversity. A different more potent same-sex pairing cannot further our society's genetic diversity. They are void of the goal of marriage: biologically predicated kinship.
The societal investment in same-sex relationships to the extent of calling them marriage does nothing to further the cause of marriage: the genetic diversity of society. They are largely privately beneficial relationships compared to the societal benefits of permanent heterosexual union.
Consummation is the fulfilment of the inaugural legal intention of a contract. The law neither dictates exactly when this should happen, nor that it must result in offspring, but it does view it as a reasonable legally supported expectation of both parties to marriage. At the very least, the vow of fidelity is a commitment to the physical act of kinship-forming union with one person. There may be other acts, but 'ordinary and complete' intercourse is the minimum expectation (case law: D v A (1845) 163 ER 1039)
The fact that there are exceptions (through age and impotence) is an issue of individual incapacity that cannot be established in terms of changing universal rules for constituting all valid marriages. It does not mean that marriage should be constituted for the exceptions without qualification.
In fact, this is the converse accident fallacy: that one carefully qualified exception justifies an unqualified change to the general rule.
If consummation has never occurred owing to the permanent incapacity of one partner, or the refusal of one partner, it opens the marriage contract to the possibility of annulment: invalidation from the date of the wedding.
Annulment as a remedy.
Is annulment important? Annulment means that the requirements of the contract have no legal effect. It is not simply an aspect of marriage law, any contract can be voided for fundamental incapacity or non-performance of either party. This is fundamental to all contract law.
Void ab initio (from outset) contracts are those which demonstrate that at the outset both parties lack the capacity to be bound by the common legal expectations of the contract. The difference with marriage is that those expectations are established by long tradition and case law.
Void marriages are invalid marriage contracts. For instance, if either party is under 16, already lawfully married, if parties are not of opposite sex, or within prohibited degrees of relationship, the constitution of the marriage is deemed invalid from the outset.
Voidable marriages are open to be avoided by either party, unless the petitioner knowingly accepted the incapacity or deception, once it was revealed. There are defects of:
1: Form: the marriage was not solemnised lawfully;
2: Contract: if either party lacked the intent or capacity to enter into a lifelong kinship-forming sexual union, as evidenced by consummation;
3: Consent: If either party was coerced, or deceived, or mentally incapable, so that they lacked willingness, and therefore lacked intent.
Annulment releases the petitioner from any legal claim from the respondent to divide assets equally or provide on-going spousal support. It is as if the exchange of consent had not occurred. It may be granted immediately and back-dated to the wedding ceremony, whereas divorce currently requires a minimum of 1 year’s marriage, 2 years by mutual consent, 5 years without consent.
In spite of secularisation and 'no-fault divorce', if divorce is the only remedy for an innocent party, deceived, or denied coitus as a reasonable expectation of marriage, it carries an unacceptable stigma that the petitioner's behaviour in the matter was not completely above reproach.
Even if non-consummation was treated as evidence of unreasonable behaviour, divorce would still make the petitioner liable to claims for division of assets and spousal support. However small the minority, it is grossly unfair to force those who would have petitioned for an annulment to endure the stigma of divorce. Voiding the marriage is the proper remedy for deception, duress or refusal or incapacity to consummate.
Annulment is an important remedy for voidable contracts of all kinds, including marriage. It should not be abandoned to provide a consummation-free definition of marriage. It is not fair to re-define consummation without gender references (which is too vague and open to judicial misinterpretation). It is not fair to remove consummation as a ground for voiding marriages in which one partner denies or is incapable of sexual union.
What you can't do is have disparate standards of consummation for the single estate of marriage, whether it is entered by civil or religious means. Just as there is only one status of British citizenship regardless of whether it is entered by birth or naturalisation.