We have and more. Things like Iran-Contra were all about supporting rebel factions as well. Hell, look at Bush, we run wars to overthrow regimes, and then have no plan on how to make a stable government in its place. We've done some pretty bad things, we do some pretty bad things too. It does need to stop, I don't know how much money we spend interfering with the elections and governments of other countries, but it's probably substantial. It needs to stop.
But does the fact that we mess with the elections of other countries mean we shouldn't be worried about other countries doing it to us? Hell no. That's a ridiculous and fairly stupid conclusion. It should be a slap in the face, the wake up call of "hey, we don't want it to happen to us, so we need to stop doing it to others", but we shouldn't be apathetic when it happens to us. Particularly coming from such a long time foe as Russia. And those connections/influence do need to be investigated and if there was something there, we need to punish those involved and find ways to isolate our system from outside influence. That's obvious.
Is this the new spin the Trumpetters are going to use? "Hey, it doesn't matter if Russia interfered and somehow got Trump into office, we do it to other countries all the time?" Not really a strong defense for the President.