Well, all memes are possible to change. They're just ideas. Software. The difficulty level is an open question, but the bare capability isn't controversial. So when people talk about impassable limits, I take them to be referring to supposed genetic limits -- genes are commonly supposed to be adept at putting strong limits on people.

Here is something relevant I wrote, about changing emotions (raw emotions aren't memes, but ways of interpreting and reacting to them are memes. emotions can also be triggered by ideas or memes.):

http://fallibleideas.com/emotions

The basic, overall problem is that parents and educators are extremely coercive and destroy the ability of (most) children to think for themselves (to a good approximation -- again, it's possible to recover). If you'd like to discuss that more, I'd urge you to come post your thoughts or questions on this list and I will reply (HN is not a suitable forum for longer discussions):

http://groups.google.com/group/taking-children-seriously