Competition is a fact of commercial life. It establishes boundaries, for sure, but competitors need not be enemies.
Really none of his business if you want to do this. If more feeders are easily available, there will be more people keeping herps, and more business all around.
Complete lack of feeder rodents around my area is a top reason why I'm not keeping any snakes. I've considered raising my own, and raising more to sell (what a great way to meet others in the hobby). However, the rodents need a heated space in the winter, and that is NOT going to work in our tiny house!