People are more than welcome to associate and speak out with regards to a particular cause. In addition, those people would be able to contribute to candidates as individuals, but the group itself would not have the ability to give any funds over and above what the individuals themselves could give. I would not take away the rights of the people to organize to promote a political cause, just their ability to give money to candidates over and above individual limits.
No, but I would not be taking away the rights of those people to contribute to who they want, just the ability to have a special interest group contribute more than those individual limits.
The problem is that unions and associations already rarely give more money than what what individual members can give. For instance individuals can give up to $5,000 (If I've got the limit right since McCain Fiengold) for a presidential campaign. If you've got an organization like the NRA with something like a million members that means that the NRA could give up to $5 billion to a presidential campaign. There's no way the NRA has $5 billion to give and even if they did they probably wouldn't even if the candidate said they would do away with every gun control law. Associations exist to help collectively advance goals that individuals have but since its difficult for any individual to keep track of all of the candidates and legislation around any particular issue they rely on an association to handle that. So I could either spend all of my time researching every single candidate running for Congress to see if they agree with me on civil liberties and send them a small check or I could just send one check to the ACLU and have them donate that money to candidates who they believe will stand up for civil liberties. Its my money eventually going to the candidate but I'm using the ACLU to do the reseach for me to identify the candidates.