Rubio is not going to be marginalized by this. If birthers had a clue they would just shut up. Birthers are quickly labeled crazy and worse by all media and all reputable news outlets.
If that is the case, then those media outlets are not reputable. If they are slandering people for just asking for general information, they are not news worthy organizations, but propaganda arms.
Which is why the birth question is the right question, and birthers are absolutely on the right track. As the old bomber pilot would say, "If you're getting flack, you're on target."