There is no need to open up civil partnerships to opposite-sex couples; a basic civil marriage in a register office is no different to civil partnerships.
The arguments against this are that marriages are patriarchal, maybe, but I cannot see society treating civilly-partnered straight couples as any different to the married. Remember, the whole point of CP's is that they are the legal equivalent of marriage.
As for the couple themselves: surely the quality of their relationship is not dependent upon their legal status and they can arrange their relationships as they wish?
Now I can see why people would be against marriage AND civil partnerships but to favour one over the other makes little sense. There's no discernible difference.
Let's look at the differences:
Cannot dissolve cp's because of sexual unfaithfulness, can in marriage. Surely in cp's this could be classed as 'unreasonable behaviour'
CP's don't require consummation. Marriages do. How can you prove this either way?
Unless a law is passed to examine people's genitals, how do we know? Surely to pass a law would be anti-feminist in the extreme? I think so, anyway.
Sorry, all this 'equal marriage' stuff does my head in. Marriage is a legal contract from an objective viewpoint and as cp's are virtually identical to marriage and a relationship is what the couple make it regardless of marital status, I've no time for it.
In fact, I've signed the coalitionformarriage petition NOT because I am religious (I'm an atheist) nor homophobic, but because I feel the whole thing to be a big fat waste of time and effort.