Why go to an event where there is not even a pretext of objectivity? Add to that very few people will see it and the only thing you would be doing is giving Levin credibility and it becomes a no-brainer. Rubio would be better served going to another rally.
For the same reason I've always thought Republican candidates should continue to go to crap debates like those put on by the liberal media.
Americans need to know how a Presidential Candidate will handle opposition, disagreement and outright hostility....to give us insight into how they would deal with America's foreign enemies.
If they are too chicken to even show up.........I think that's a good "tell" also.