I've always been very pro-communication, and I've always kind of felt haeting goes against the whole idea of communicating your sentiments in a clear, unambiguous and specific way. If you simply agree with what someone said, lieking is a simple and efficient way of just going "+1" on their comment, without cluttering threads with annoying, meaningless "+1" posts.
If you're going to haet a comment, however, to me it seems obvious that there is at least one particular element of their post that you have something to say about. Haeting it only contributes to causing a negative feeling in the person who receives it, without giving them any explanation as to what they did to deserve it.
I can sort of see why Facebook and Google+ (and other social media platforms, I assume) have refrained from implementing such a feature up until now (and are continuing to do so); they probably reckoned - rightly, in my opinion - that it would cause more harm than good as far as social interaction goes. The keyword here is "interaction": haeting is basically a one-way "screw you and your opinions", in my view.
In contrast, lieking is more like "here, hi-five bro", and despite also being unidirectional, it's fine (or "not as bad") because you can't really discuss, debate, or voice your disagreement over something that you precisely agree with in the first place.
So the bottom line is: keep the liek, ditch the haet.
(Incidentally, that piece of advice also applies to life in general. (: )