So whats to stop someone from getting the mod and then posting it for free elsewhere. Like really its a mod there's no drm on mods.
Also this is absolutely a terrible idea not because I'm against paying for stuff but because most mod makers are fucking insane like really head on over to the minecraft mod forums and look up what happened when the yogbox came out or look up the Skyrim Gategate meltdown by Arthmoore. Really while a good number of modders are people doing it for fun most of them are downright crazy and the mods they produce are for stuff like making their perfect skyrim waifu, that is lore friendly, and happens to have buttplugs in it. Modders are weird man like head to nexus turn safesearch off and click the best of the week and be prepared to bleach your eyes out.
Just don't support the people who make those types of disturbing mods. There are a shit ton of mods made by different people that just improve the game: better ground textures, rebalanced skill tree, better ui, better weather, etc. You shouldn't paint all modders with a broad stroke of paint because a small group of people make very questionable mods or there have been infamous incidents with some of them. I'm pretty sure that those types of questionable mods wouldn't even get onto the workshop anyway.