From marriage to relationship recognition

Continuing the thread that I began with these letters and followed up with this dissenting email from François Brutsch, I draw your attention to Peter Tatchell's argument here:

While this milestone [civil partnerships] is a cause for celebration, it also has a downside. For the first time in modern British legal history, instead of repealing discrimination parliament has reinforced and extended it. Civil partnerships are for same-sex couples only. Straights are excluded. Conversely, marriage remains reserved for heterosexuals, to the exclusion of gays. The differential treatment of hetero and homo couples is enshrined in law. Welcome to segregation, UK-style.
.....
Imagine the outcry if the government prohibited black people from getting married, and established a separate partnership register for non-whites.

I don't see how the logic of this argument can be faulted. Tatchell goes on to propose a 'new legal framework of relationship recognition' that would broaden out to embrace any kind of caring relationship - a proposal, I have to confess, that is new to me.