An interesting article. I think it is a bit rich for any organisation to state "we abide by the law" while at the same time saying "we can't be responsible for the actions of individuals". In the same vein Hammas is a political organisation, just because a few members take action that, I'm sure would be morally correct for them, which amounts to terrorist acts for others, I'm sure Hammas gets away with the same rhetoric as PETA.......or maybe not.
I don't believe it is wrong to kill a dog that has attacked a human, further there are laws that put responsibility back to the owner (if there is one) to pay for damage/costs incurred as a result of their dogs actions. If taken through court, the owner can be fined and the court can order the destruction of the animal. Law enforcement agencies here (northern territory australia) have the legislated power to destroy dogs on the spot if that is deemed the most appropriate course of action.
The laws of Canada may be similar to those found here in NT Australia. Here, the owner/occupier of a residence has the legal right to evict a trespasser, by using reasonable force if necesary. Similarly, there is a legal right to defencive conduct, where, if you are defending yourself (or others) and also for removal of trespassers.