Sikh's can't eat halal or Kosher at all (so many Sikh's have been forced unwillingly into vegetarianism). Many religious people although not strictly forbidden to eat either do not as their conscience struggles with the idea of eating food which has gone through the rituals of another religion. Just like Catholics are allowed to take CofE communion but many choose not to as it is a meaningless act which they view as a sham. Many people choose not to eat them for welfare reasons. Okay, some of the meat might have been stunned but you don't know. Would you find it acceptable to ask a vegetarian to eat something which might contain meat on the grounds 'a lot of them don't contain meat so you might as well chance it'? Many people feel that is does not provide the same level of flavour, which supporters vehemently deny turning a blind eye to the fact that you can switch on the TV any given day to find a TV chef extolling the virtues of meat in blood and maturing for flavour, neither of which you will get with halal meat. And a quick Google will spring up many Muslims who have eaten both and swear they taste very different. And y'know, some of them might choose not to eat it because they object even to indirectly supporting an ideology which on a widespread level treats women appallingly, persecutes those of other religions on a massive scale, promotes cruel and inhumane punishments, breaches human rights on a huge scale and persecuted, harasses and often murders those who choose to leave the religion. Which is not that different from boycotting Israeli/kosher goods. (And I note those who whinge about kosher not being avoided often fail to mention that there is a far more pervasive boycott of Jewish and Israeli goods which they choose to overlook). Bit of course the left wing bundle a huge and varied list of reasons into 'raaaaaaacism' (like they do about fucking everything which doesn't fit into their narrow list of acceptability).
Personally I boycott Israeli goods because I think they're behaving like a bunch of knobends at the moment particularly over settlers and violence against the Palestinians. But I also avoid halal wherever I can. For reasons which include some of the reasons above.
I have a huge objection to the lack of provision for people to make an informed choice over whether or not to eat halal or not by refusing to introduce a compulsory labelling system. And by halal becoming the default option in many places like schools and hospitals.
Now many left wingers now use the stock response of 'well if you don't want to eat it go vegetarian'. Which is massively hypocritical, because this is what Muslims were told for years and the same people demanding others go veggie were incredibly cross about this and (of course) found it dreadfully racist that Muslims should be told they had to go veggie. But apparently it's fine to tell other people the same. Because we are all equal but apparently some of us are more equal than others. And those of us who are more equal tend to be whichever group the left wing has decided is their current pet project.
It doesn't really matter if people's reasons for not eating it are religious, political, culinary or because they have a fear of things which begin with the letter 'h'. Everybody has the right to make informed choices about what they eat and a compulsory clear labelling system should be in place. This would probably also benefit Muslims as it would give them greater choice when shopping.
Basically what this boils down to is yet another subject on which the left wing have decided anybody who won't follow their precise orthodox dogma has no right to a view must be bullied and intimidated into silence by dragging out the tired old 'racist' trope that nobody apart from themselves takes seriously anymore because their exploitation and overuse of it has rendered it essentially meaningless and a bit of a joke.