In Morrowind and Oblivion the "good" people who worship the nine divines, hate daedra and necromancy, yet they summon undead or daedric creatures. Wouldn't that be considered evil magic? A bit hypocritical, no?
There is no good or evil in TES, only shades of gray.
Magic is not inherently evil, its how you use it. Just like any other tool or weapon. Usually, its a matter of perspective. A nation using hordes of Daedra against another nation would be seen by their enemies as evil summoners of evil daedric spirits. Their allies would see them as intelligent and skilled summoners.
As for the Daedra, they aren't evil or good anyways. They do what is best for themselves or their lords, just like most mortals.
As for daedra turning on their summoners, I think I'd be pretty pissed off if I was relaxing in my domain and then got teleported to another dimension, forced to fight something, and then probably die, return to the soup of Oblivion for an indeterminate amount of time, then reform and maybe have to do it again. Even worse is if I get permanently forced into submission, as with the famous dremora Anhaedra (and all of his colorful dialogue).