I try not to feed live foods to my fish as I do think it is unfair on the smaller fish which is going to be eaten.
I would never consent or help advise someone to let a guppy/platy/molly fry to any fish.
But it is nature
I feed mine live bloodworm's once a month as a treat I dont feel to bad that way.
Everyone is different , In that way I am a bit of a softie! I would advise you stop letting them breed and feeding them to your betta. You could raise them which is fun and then if you dont have enough room donate them your LFS
Make sure you have enough space to let them breed though and live happily otherwise I would just pack this whole business in! You could buy a bigger tank some can be cheap! Pop a heater in and a filter and your laughing! I use to have one in my shed ! I got too attached to them so I made sure they had everything they required and they were happy!