I think the lack of controversy around the Unchained Summoner, among with more conventional summoning, is as stated before: the creature is entirely under the summoner's control. More importantly for me, though, is that while evil, demons, devils, and the like are still "natural" entities, while all types of undead necessarily are perversions of the natural order. When you summon an outsider no living creature is necessarily harmed, while the creation of undead is an inherently harmful act whether or not the undead is hostile, or even sentient.
At least, that's my perspective. Besides, our meta information tells us that no PFS character can be of evil alignment, so if a teammate starts summoning Qlippoth or whatever you can rest assured he probably won't tell it to eat you.