Bark collars are cruel in that they inflict discomfort and/or pain as a method of stopping barking. There are better and more humane ways to deal with barking that don't hurt your dog and also will address the root of the problem. Bark collars do not address the reason for the barking.

Are vibration bark collars humane?

Using nothing but gentle beeps and vibrations, humane bark collars eliminate the injurious electrical discharge of a dog shock collar, while still providing effective training against nuisance barking.

Do bark collars traumatize dogs?

While many people will say that electronic collars don't really hurt the dog — “it is just a tickle, a spray, or a little stim,” — they would simply not work if they weren't at least somewhat aversive. The dog must want to avoid the spray or shock, or there would be no motivation to stop barking.