I agree it's not as easy as "can't go past the base" but the outcome should be able to help tell you what's going on.
Stealing second and he goes past the bag. He's either going to try to get back to second or continue onto third. That establishes a new baseline in both situations. The baseline cannot be extended continuously past the bag. On a bang bang play at the plate and the runner misses the plate he has the circle to create a path back to the bag. I can see this being applicable in a steal situation. Plus in a steal the fielder is in front of or on top of the base. Going past the bag doesn't put him in harm and there's no chance to continue a play to first for a double play. If the throw from the catcher takes him into the path of the runner then it's just a train wreck. Like I said earlier you can't take contact completely out of baseball.
As for first base I think it's apples and oranges. There are established rules for this situation. But if you want to make it analogous then the the throw causes the fielder to stretch towards the outfield but the out is made. When he leaves the base he's past the bag. There's a runner on third trying to score. What would happen if the runner slid into first and went past the bag and took out the first baseman like Utley did? The call is going to be interference and probably an ejection. Each base has it's own ways of handling these situations.
I do completely agree with you that the suspension is wrong since he technically didn't break a rule. I still believe if they had called interference off the bat nobody would have said a word.