Depends on the trap I would say. One that generally rapidly kills is fine but say sticky traps are cruel. Traps where the animal is stuck in place unable to move and slowly dies of dehydration/starvation that is just sadistic.

That's a pretty popular viewpoint to be honest. Glue traps aren't even particularly effective, and neither are they particularly reusable. So in addition to being cruel they just aren't a good deal for the money you'll spend.

Drown traps (using any number of mechanisms to dunk rodents into a bucket of water from which they cannot escape) might be a bit rough ethically though I think much better than glue traps. Additionally they're many times more effective, fully re-usable, and you can make them basically for free with a few scraps laying around in your garage. One method that works well on mice and other small rodents (though not so much on norway rats which are incredibly clever) is as simple as floating a layer of seeds on top of the water. The rodents jump in to get the seeds, not realizing that the seeds were floating on water. A bag of bird seed, a bucket and some water are all you need for that sort of trap and although death isn't instant, it's a lot faster than with a glue trap.