My immediate concern with tags is descending into what Twitter has become: hashtags have been meaningless for a long while since there’s too much wrongly tagged stuff, different communities often use the same tag for different things, or there are ten tags all for the same thing. All of which means we’d need some form of moderator role that handles tags, and while I think it’s doable, it might take some trial and error to figure out how exactly we divide tags between moderators, how tags are proposed/created, and how tags are grouped/combined (e.g. food, foods).
Subsidies are an incredible tool when used well, like when they funded a bunch of utility cooperatives that electrified rural US. Maybe you’re asking why we should because propping up the car industry when public transit and bike infrastructure should be subsidized instead, rather than challenging subsidies, though.