There's no excuse for not being able to support. If you can play adc, then you should know how to support by proxy. And considering in draft pick, last pick is generally more likely to go support (seems like people like supporting more nowadays, tho) it's wise to at least know the role. There's a difference between not being good and just never practicing it at all, so you should at least be the first so you're not dead weight for your team. Supports are important for the team (there is a reason it's in the meta) and we need to remove the mentality that they aren't and can't affect the game meaningfully.
As for jungling, I will admit it's a more difficult role to pick up (supporting takes awhile to master, not to diss them) than the rest. There's more to it than ganking lanes, farming, and warding stuff. Different champions jungle different, and there's more objectives than just kills to be done. So I'll give you that. Giving someone the role who has no idea what they're doing removes all pressure from the map, and will heavily increase the enemy's chance of winning. So I'll give you that.