It's very effective. It creates a second layer of resistance to contradictory evidence. Firstly, people don't like being shown they were wrong, which is the first layer. The second layer is that they got the opinion from someone that they like that has a history of making them laugh, fond memories and the like, and they don't want that person to be wrong either.

Luckily, as far as I've seen, Jon Stewart was the last one to do it well. Everyone else's minds are too fucking warped by the bullshit to land a joke anymore.