Many people agree that some of those ads were misleading. Nonetheless, the ads brought large numbers of African-Americans to the polls in several states. Without large black turnout in the future, the Democrats will be in electoral trouble. For those reasons, many Democrats may want to vote against the bill. For those who value free speech, the great danger now is that many Republicans will decide to support the McCain bill because they realize what immense harm it will do to the Democrats.
Political principle is one good reason.
The Republicans have always said they opposed McCain because free political speech was a right. The GOP should remember that the principles at stake in the campaign finance fight are above partisanship. In America, the right to speak requires money. If government restricts spending on campaigns, it is trying to limit freedom of speech. That is unconstitutional.