I'll second support being the hardest role. A lot of the stuff they have to do could be pushed onto the AD, but the AD is typically someone who's superior at the purely technical skills of last hitting and positioning. Support lends itself more to a strategic mind for many of its responsibilities, but still requires knowledge of all the technical stuff so you can protect your team.
For instance, a support needs to know when every jungler in the game can gank bot (from blue and purple side) and needs to know where they can gank from (in the case of Shaco/Nocturne ward jumping, or people crossing walls). Support shares a lot of responsibilities with the jungler - always paying attention to where the enemy mid/jungle are for potential ganks and dragon attempts, warding most of the SE section of the map, aiding in counterjungle attempts, and so on.
I wouldn't say it's the hardest role, but I would say that it IS, along with jungle, one of the most underappreciated roles. Here's the thing: yes, you might not say GJ to top lane or to mid lane or even to the ADC, but they
do that on their own. Support and jungle are there to help the ADC/generic lanes out, so of course they should receive gratitude. When I jungle, I thank when mid and top leash, right? But top and mid don't help the jungle out at all. The ADC doesn't help the support at all (it...varies, probably, depending on who you ask, but I generally initiate bot lane fights as support, not the ADC). Sure, when top/mid/bot win their lanes, that helps the team as a whole, but that's covered by a "gj team" at the end of the game if your team did well.
It's not unreasonable that the jungler and support expect thanks, since they help others without expecting or receiving much help in return. Before the laning phase ends, anyway, though. Which is still arguable since one of support's jobs is to peel for the ADC in teamfights.
To be honest, my personal opinion is that jungler is the hardest role, just because you're expected to keep watch over everything and still maintain a good clear speed AND gank lanes on top of it all. Supports just keep watch over the map and on the lane for aggression opportunities. I enjoy playing support, but I absolutely abhor jungling, even if they play more of a role later on in the game. Also, everybody rages at the jungler. Everybody. Even the times when I'm not jungling, there's always some entitled instalock top lane or instalock mid lane who's complaining about jungle ganks.
Support actually feels like an easy role to play for me. In one of my most recent games, I saved my jungler's ass by a well placed ward when LeBlanc came to gank him in the jungle before level 6 and secured First Blood for him, too, from the LeBlanc. That LeBlanc was miserable for the rest of the game because I wouldn't let her do shit in our jungle or bot lane. Admittedly, though, I cannot, for the life of me, play Nunu, Nami, or Janna. Nami doesn't feel right and carries never know what to do with the steroids those supports provide.
That's the way I'd probably try playing it, though. Have fun getting past resurrection tower, a beer tower, and a spawner. Actual players could probably do it, though. The bots always wander around taking care of the miscellaneous enemies before trying to kill the resurrection tower, so they always take lots of time getting through it.