The points are:
1) There are parts of every halal/kosher carcase which are not eaten by Muslims/Jews
2) These cuts must be sold into the general meat supply to keep the price of halal/kosher meat as low as possible. If these unwanted cuts were not used for human consumption, but sent for ( say) petfood, the price of the religious meat would rise colossally.
3) If non-religious people are to buy religiously-slaughtered meat, the sellers know it is much more likely to sell if Not marked. Some meat-eaters don't care, but the sellers of such meat know that enough buyers would care and would refuse to buy, and there would be a problem with over-supply of this meat.
I do care very much that religiously-slaughtered meat can be foisted on me without my knowledge and against my will, just to keep prices down for the religious people.
And I don't see why I should have to stick to pork and fish.