Earlier quoted context omitted.
I don't think it's as simple as "Iran is probably the worst country on the planet when it comes to supporting terrorism." Every powerful country uses violence to advance it's political goals. Every powerful country kills the civilians/citizens of other countries, publicly expressing varying amounts of regret.
The parallel comment by salimmadjd has a point about Pakistan maybe being even worse than Iran, when it comes to terror support (I do doubt that Saudi A as a country is worse). I might stand corrected, there. >>Every powerful country kills the civilians/citizens of other countries To explicitly target civilians is serious because it breaks the laws of war, etc. Democracies generally don't do that.
Democracies generally try not to publicize doing that. Unless it's done with drones apparently, then you brag about it.