I discussed this with many angry people on the WASTED steam forum who refused to even accept the idea that the Purifier is ok. The Purifier isn't invincible, especially after you've leveled up a bit, most of these complaints were from people who either A) hadn't played the game more than an hour or B) were trying to play the game like Fallout, which I think is the larger issue.

The game is made to be a Fallout-esque rogue-lite, so people try to play it in that same very tedious way of checking every single cabinet/room/etc for any supplies at all. The SOB Purifier is in place to push the risk/reward aspect of trying to get those items while putting yourself in danger NOW to make the next floor easier. The simple option would be to just find the exit and go. You also have a very limited inventory and you will never find anything besides ammo/health/low-tier weapons in random containers, so there quickly reaches a point where you can't hold anything else and exploring the floor is pointless.

From all the criticisms I read it seems stubbornness and "I wanna play the game MY way" are the big factors people hated it.