There's lots of reasons why Bard is considered a terrible champion by many players. His kit encourages roaming and most players don't know how or when to roam correctly, his abilities were underpowered like crazy when he was released (and might still be, depending on how this patch goes), and his early game isn't as strong as most other supports (when they have the most impact on a match). Another of the main reasons is that a bad ally Bard ult can completely and utterly screw you and/or your team over with no choice from you. That's horrible. No one ally champion should get to decide your teamfight for you like that.
When Blitz hooks the wrong target, you can GTFO (most of the time). When Ali headbutts an almost dead enemy away, that's rough but doesn't end up killing you. Kalista ulting without warning is heavily toxic, just ask Riot about why they had to remove the option to refuse binding yourself to her. Urgot ult.. well there's multiple reasons he's got one of the lowest pickrates; the difficulty in using his ult correctly being one of them.
Have it implemented similarly to Thresh's lantern for all I care. But... just look at how rarely people take that damned lantern, even when it would save their life.
One of the most frustrating parts of the game is throwing out that lantern and watching your teammate refuse to click it. But if you make him click it, you're taking control of his champion away from him without his consent (even if it is to save him from doing something stupid), and that's even worse. Nobody should control your champion but you, unless you willingly give it up by clicking that lantern.
People can mess things up just as easily themselves. Honestly, in the matches I've played with what this board seems to consider the ultimate troll, Bard, I've seen more helpful ults than "troll" ones. Enough that I'm actually strongly considering picking him up, because of the potential that's there if played well.
Consider yourself extremely fortunate then. I would advise playing the lottery in the near future, as lady luck obviously has a hard on for you.
In general, I think someone is just a liable to mess things up for their team with an ill-advised Blitzcrank hook than what I described in the OP.
That's incorrect. Blitz can make a bad pull, but most of the time you can react first since you can see the unit getting pulled. If it's a marksman, pile on. If it's Amumu, get away from Blitz. Chances are Blitz is going to hit whoever he hooked with his knock up anyway, giving you extra time to reposition yourself accordingly. Bard ult gives no such mercy.
P.S. Is there ever a suggestion thread on here without a post about the ways in which said suggestion can be abused and why that means Riot shouldn't even bother?
This is League of Legends. If something can be abused, it will be abused. Multiple times. All the time. Because this game has one of the worst communities this side of Call of Duty. Every step Riot takes has to be carefully examined for any possible exploitations or loopholes, even moreso than other game developers. Pointing out the flaws in people's suggestions isn't them being rude, it's required.