[1] https://en.wikipedia.org/wiki/New_York_Times_Co._v._Sullivan
They just can't vote.
But, in all fairness, that's not their primary purpose, it's merely a side effect of their overall utility. Most people in most corporations are decidedly not criminal, and they don't behave as criminals.
For example, while they can break the laws like people, corporations are not punished the same. When was the last time a corporation was "executed" (e.g. corporate charter revoked)?
Once you give the government a tool to restrict speech / spending, it will be used to cut both ways.
Although donations to the wrong political group can certainly get you in big trouble today (if you're willing to stretch the definition of 'political group'), so...hm.