Completely agree, but if you're going to blame MinnowBooster, you may as well take it to it's logical conclusion and blame Steemit. It's my view that comment voting shouldn't even be possible - a tipping system would be much fairer. The MB devs didn't design the system to help leeches, but as long as leeching is possible and there are leeches everywhere, there's not much they can do.
I'm not sure exactly how many renters do this, but judging from the support channel, I think it is only a small minority.
I'm not exactly blaming minnowbooster, it's a great idea for those who would use it morally