Though I've often joked that I'm in favor of legal recognition for same-sex unions because I want gay people to be as miserable as straight people, I didn't have any notion of forcing anyone, hetero-homo-bi-trans-asexual, to have to undertake marriage. People who want to make the commitment should be able to do so regardless of their gender, but they should make it voluntarily, like joining the military. Drafting people into the bonds of matrimony when they haven't chosen it strikes me as an invasion of the freedom not to marry nor make any reasonable facsimile thereof (civil unions, domestic partnerships, etc.).
Yet that seems to be what Britain's Law Commission proposes in the guise of giving unmarried couples' relationships "rights in line with those in marriages." There's no suggestion that any discrimination prevents these couples from getting married if they wish to do so; same-sex unions already are recognized, and if the cost of a marriage certificate is so prohibitive, the government can issue income-based waivers. People who do not to marry/ unite/ partner are deliberately choosing to live outside the existing legal paradigms, and this choice ought to be respected. Presumably the UK's Child Support Act is similar to the American regime, in which a baby born out of wedlock nonetheless claims monetary support from his biological parents, so this doesn't protect children of unmarried couples. Many American states also provide for common law marriages after several years of cohabitation and publicly holding out the co-habitor as a spouse. Though not a legally registered marriage, calling someone your husband or wife is enough of a decision that I'd countenance it as the cheap ass-backwards version of getting hitched.
The Church of England conditions its support for the Law Commission's proposal on maintaining the "unique position of marriage," but I want to maintain the unique position of shacking up. Even in England, longterm childbearing cohabitation is not the norm; more people who undertake such non-legal commitments make a legal commitment to each other than those who do not. Let people who decided to deal with the questions of "You're not married yet?" and "How long are you just going to live together?" do so instead of imposing the rights and responsibilities of marriage on them.