I don't think that review was particularly hateful at all. A little insensitive, maybe. But the person is expressing how they feel about what I assume is a perceived militant homosexual/leftist agenda being forced upon them, not anything negative about homosexuals themselves. As I haven't seen the film yet, I can't comment as to whether the portrayal of the gay couple seems to be promoting such an agenda, or seems excessive in any way. But from the looks of it, I don't think so.
Although promoting such an agenda does seem to be somewhat of a popular trend in media lately, it seems this person is reaching and overreacting. It's very annoying and somewhat disheartening when conservatives go searching for bad guys where there are none, and whining about things, much like the leftists they mock for doing so.
As for the inclusion of a homosexual couple in Covenant itself, it seems pretty natural to me, and not at all excessive. When dealing with a mission of colonization, couples and sex are a natural part of that. So it makes sense that among a bunch of straight couples, there would naturally be a gay couple, as homosexuality is not at all uncommon.
The only thing I can see going against a gay couple in this situation is that they're not ideal for procreation. But that doesn't take into account what other value they can add to the mission, which really depends on their personality, skills, merits, etc... Also, they add 2 more sets of genes to possibly be used if things became dire and such an action was necessary.
I don't think the inclusion of a gay couple in itself is progressive, as homosexuality in media is pretty commonplace nowadays. But the portrayal of the couple might be progressive, as gay characters can still be somewhat of a stereotype in media, so a portrayal that strays away from that could be considered progressive.
