It f*cking doesn’t.
Halal basically means the following: That an item of food is free of pig products, free of blood, and free of alcohol – all of which are forbidden under Islamic dietary codes; similar to how Kosher foods meet Jewish dietary needs (which Halal is often used as a standard, for convenience, as both Kosher and Halal are very similar). To put this even more basically: Halal (in an Islamic context) = allowed.
No, Halal certification doesn’t fund terrorism, either, just incase you were wondering; and anyone who says that it does is likely a conspiracy crank.
If you are an animal rights activist and are against Halal slaughter – then congratulations on being a part of the only group of people who has a valid criticism of Halal slaughter (your argument against Halal slaughter also carries more weight if you are vegetarian or vegan). However, if you are using animal rights as a guise for your own blatant bigotry, then you are a dick. End of story. (Unfortunately, most “animal rights activists” against Halal fall into the latter category).
Furthermore, because not all Halal certified products are meat products, the concerns of animal rights groups only extend to the Halal method of slaughter; not all Halal certified products.
For everyone else, Halal doesn’t adversely affect you, just like the Heart Foundation Tick of Approval doesn’t adversely affect you, so quit flogging your dead horse to no end about it pretending it does, because it doesn’t, you gullible moron.