Except that speech does not equal money. That's part of the blowback on the Citizen's United ruling from the Supreme Court. You have a right to support your candidate but there is a general public consensus that the use of money to buy a candidate's way to victory is immoral, unethical and should be illegal.

You are correct that you have 1st amendment rights to shout it from rooftops, however the use of public spectrum broadcast networks is very very different.