Exactly. This also applies to stuff like voice chat. It's ridiculous to limit champion design just to prevent people from trolling. The way the game is set up, they are fully capable of doing it already. In fact, just the fact that dying gives gold to the enemy is enough to enable game-ruining trolls. The fact that impactful spells exist at all opens up a whole new avenue for trolls: they can just whiff ults on purpose.
Heck, look at Dota 2. Keeper of the Light can teleport allies to his location, which can include in the middle of the enemy team. Io (or Wisp) can teleport himself and an ally anywhere on the map...including the enemy base. Nature's prophet can teleport himself anywhere on the map as well. Faceless Void's ult is basically a stronger version of Bard's ult. Zeratul from Heroes of the Storm has an ult identical to Bard's except it isn't a skillshot. Pudge can Blitz hook allies to him and into danger. In fact, why pick specific heroes at all? Just buy a force staff (perhaps wasting gold that could've been spent on more effective items) and push allies into the enemy team!
No one needs to troll in Dota 2 or HOTS using Io, KotL, Void, Pudge, Zeratul, force staffs, etc. Chances are, if someone is going to troll with Bard, they've already been doing it using other methods.
This is also why I'm an advocate for voice chat ingame. People flame all the time just using their keyboards, but somehow using your voice to say the exact same thing is worse? The outcome is exactly the same: ignore and/or mute them.