The question is not ‘why are roaches disgusting?’ (which they are), but rather ‘why are we disgusted by roaches?’
Good question. Probably because they move so fast,they have TRULY yucky feelers,and they spread disease. I am scared by small creatures that move faster than I do (not including my grandkids). The fact that they go crunch when someone steps on them, adds to the ick factor, and that black or brown carapace is just awful to look at. Certain other bugs do NOT disgust me, like caterpillars, ladybugs, but anything looking like a roach or a worm or slug, makes me sick. And don’t get me started on SPIDERS.
As to the boric acid – it is well known as a successful roach remedy, but HIGHLY toxic to people and pets, so be careful if you have small children or grandchildren around, or a dog or cat. It will wipe out the colony within a week, as the roach gets it on its legs and brings it back to the nest, where it dies, and the other roaches cannibalize it and also die. Or so I was told by the person who recommended the BA as a cheap pesticide. It also slows them down so they can be caught, if that is your wish. I would not put BA near open food.