It's true, but there are so fewer novels with apocalyptic theme...
I am reading all kinds of genre if the novel worth it. And I can't say I am a yaoi genre fan, but I am not against it. So, if the plot is good, if the characters are well designed, why not?
The reason I reply in first place was the contradiction: going to a novel tagged as yaoi and complain about this. I always read the tags carefully, as a matter of fact I don't like the harem tag at all, but if the plot is good and not centered on harem issue, I give a try.