What's up with the ganker hate? I would like an explanation from both sides pls!

So I've been watching some Ds3 youtubers, (Sol Glacies, Oroboro, Sunlight, Pineapple, etc.) and every now and again there is always a video that talks about ganker frustration.

I just want to know why it's such a hated thing?

Personally I don't find it to be that much of an issue, I always thought the point of invading was to be this kind of cutthroat no mercy type of person. In that context, I would say it's fair to be ganked up the wazoo.

The most common counter argument I see to ganking is that it's unfair, but I don't think so because invading is meant to impede the progress of a host from completing the game. Sure there are people that set up a build for PvP so they can fight others at certain levels, but unless it's arena I still don't think that ganking is that huge of a deal, in fact, I think invaders should expect it.

Anyway, that's just my spiel, I would like to hear ppl's opinions on this.

My history of souls games is all of them except Ds3 cause I'm a peasant gamer, just so people have some context about OP.