Does anyone not have any problems with taking ideas seriously?

I recall you asked a similar question near the end of the decision theory workshop. I think that every long term SIAI member has no problem with this skill (though of course there's some variance, and it's hard to know what everyone is thinking; also some are more consistent than others). Outside of SIAI there seem to be a lot less examples, but a few names come to mind. (Wei Dai is one of them.)

You mention Eliezer and Michael Vassar as people good at taking ideas seriously. Do you know if this came to them naturally, or was it a skill they gained through practice?

I have no idea about Michael Vassar. I do know that he seems to have had this skill for many years at least from various papers and comments I've seen of his that were way ahead of everyone else at the time when it came to identifying the most relevant and critical arguments. But it does seem like Eliezer was born with a natural predisposition towards this kind of rationality if the examples from his childhood and teenage years found in the sequences are considered reasonably accurate.