Well, what a lot of deeply amusing posts. Cornflakes...hee hee 
OP...your concerns regarding halal slaughter are, in fact, shared by lots of people...the RSPCA, British Veterinary Society, various farming societies, not to mention entire countries like Denmark, Norway and others.
But dare to mention it on MN? You're an ignoramus, for some reason. You're quite lucky not to have been called a racist islamophobe. (Wish I was joking).
The issue is religious exemption. In the above countries, there is no religious exemption, stunning is a legal requirement.
Not here. While most halal meat is stunned, a sizeable minority (10-20%) is not.
Boycotting won't make much difference because you probably won't be shopping in the places that freely and openly sell unstunned halal meat.
But you can campaign against it. Plenty of organisations you can join to do that.
And take no notice of arguments like, "Oh, well, all slaughter is inhumane anyway". Erm, no, that's bollocks. And if that was true, there's such a thing as degree.