And why would that be? ( Apparently closeness and feelings don't matter, but genitals do. ) Well I love Ymir and Krista separately and as a couple. I don't see any sense in picking on their ( possible ) relationship just because Ymir happens to be female. If you have any real argument as to why not only Krista, but anyone would 'deserve' a partner of the X gender just because they are of that X gender, then I'd tip my hat to you.
I don't mean to be overreacting, I just get really aggravated when people say this kind of stuff.