If some one is told not to have a dog around other dogs and they have the dog around other dogs and it attacks is it right to put the dog down?

One view
No, it is not right to kill a dog or any other animal on your own decision, you may be legally prosecuted for such action..

You must also be aware that for presenting a formal complaint, you must explain the why and how of the attack. Dogs are animals and their behavior is conditioned to territory and leadership. Who is incorrect in the case mentioned here, is the owner, not the dog. The correct action should be to restrain the dog and to oblige the owner to comply.

You may notify the owner through legal proceedings of your complaint and of your request to have his dog away from others. You may also present a legal action against the owner.

From a moral standpoint, you must also consider that it is the owner who is incorrect and the dog should not be killed for that.

The best way of action is to first notify the owner of your intention to present a legal complaint if the dog is allowed to be free from any restraint. If the owner persists in not correcting the situation, you may present a request for restraining the dog at the competent legal authorities.

Another view

The owner of the dog that attacks should be held financially responsible for injuries to the dog that was attacked, and if the dog that was attacked dies, the owner of the dog that attacked should pay suitable compensation to the owner of the dog that was attacked. And if, the dog attacks a human, the owner must face severe legal penalties.

If it was a guard dog etc then it was only doing its jobbesides dogs regularly fight my do some times does yet hes a lovely dog hes even happy to see visitors and hes great with kids too. Besides if you were warned then its due to your own stupidity