The rights of an individual to take part in political activity, whether as candidates or as campaign supporters, should not be infringed upon based on fame. If people are concerned about the influence of famous entertainers and the spectacle they bring to politics, the solution is not in preventing actors or sports figures from being part of the political scene, but rather addressing the public's tendency toward tabloid stories and surface level political analysis. This is something that needs to be addressed regardless of the participation or lack of participation of celebrities, and is a core issue in the debate for an informed political culture.
I believe popular and famous entertainers do have a right to participate in political campaigns. With popularity and fame people are often able to persuade people into making certain decisions. This is why entertainers are often used by companies in advertising. The same principals are at play in political campaigns with the exception that entertainers generally side with and support the politicians they personally believe in.
All sorts of people if they have influence are certainly entitled to participate in and contribute to political campaigns and tell us who they are voting for. On the other hand, it is our job to take their views as no more important than anyone else's and to make our own informed choice.
People follow entertainers on a regular basis, if they bring something to a campaign, its for the good. I know people like to identify with their famous entertainers,but some can be an issue for the candidate. I doubt anyone would have touched Rosanne Barr after her Anthem debacle, its all up to who the entertainer is, in the end they should help.
Popular and famous entertainers do have a right to participate in political campaigns. This falls under constitutional law, and especially under the first amendment (Freedom of speech etc). It might be better if celebrities weren't involved, but it is their right to do so if they feel like it. They're Americans.