When deciding whether you think someone should apologize or not for an action, the issue is not whether the party they offended can force an apology, it's whether you believe that person's action was wrong.
Many of the people angry about this incident believe that sexism is wrong, but advocating atheism in Dawkins' manner is not wrong. Therefore they believe the sexist should apologize, and Dawkins should not. Their opinions are consistent, and it has nothing to do with force.