Do you agree with our Constitution, or not? What you're proposing is again, a violation of the First Amendment.
To wit:
"Congress shall make no law.....abridging the freedom of speech..."
Every citizen has the right to free speech. Fictitious entities, be it a corporation, union or political action committee or whatever do not have that same right to speak for an individual. Those entities are free to speak to their individual members and urge them to give money to politicians, but they do not have a right force their members to donate to a politicians (i.e. put words in their mouth.) That decision should be left to the individual.
If you had a job that required you to pay union dues, do you like the idea of that union giving your money to politicians you do not approve of? Same goes for stockholders in corporations. And PACs are simply a way to launder money extorted from individuals through the corrupt K-Street lobby industry.
None of those have anything to do with free speech. They are just about buying political influence.
Politicians aren't elected to represent unions, corporations or political causes. They are to represent the people. Allowing those fictitious entities to bundle money, our money, and use it to buy a louder voice with politicians.