I have no issue with BPs being used as feeders. I would have an issue with someone forcing a unsuitable prey to a snake that doesn't eat other snakes as part of it's diet.
But to feed kingsnakes, cobras, etc that are snake-eaters? No. That's fine. If someone doesn't want to bother selling $10 normal males(and it does often take way more time and fuss than is desirable), and has a market/need to supply them as feeders instead, then it's acceptable to me to supply the feeders.
I have sold many normal males. But if I had a friend who had a snake-eater, I would consider supplying feeders if they were having issues finding them. Consider. Because honestly, I watch each baby emerge from an egg here and glory over every little head... normal or morph.