Yeah well, how about defining fundamental first.
People rarely change their fundamental beliefs, because they've invested a lot in them, and they're at the foundation of their belief system.
So no, it hasn't happened to me.
However, on a smaller scale, arguments have changed my mind about things.
This is interesting, although I dont see the dichotomies that some people do and when they are presented to me as real when I dont experience them as such they tend to become tedious and I feel no this binary logic is bullshit, I will not choose from the two imperfect possibilities you have presented me with when I think we're ignoring a more interesting overarching discussion.
Dichotomies which I've felt were false but others didnt included for instance socialism vs. individualism, particularly with reference to public or social policies, market socialism vs. non-market socialism, that ones a little more obscure and niche but anyhow.
I'm always pleased when I discover some transcendence of either-or thinking were it shouldnt apply, particularly if its delivered by someone who's ignorant of its existence in the first place, they look upon the thing with a fresh prespective.
A great example of this I remember was in a mailing list on anarchism which I participated in the late ninties, they were debating the differences between "lifestyle" and "social" anarchism, it was a case of never the twain shall meet and each is anathema to one another and one is true the other false, until someone who had a much more casual and apolitical interest, who was actually more interesting in cycling, asked what's this all about, when they two ideas were outlined they said yeah, I'm for both of those things then. Really was good to see how that threw a useful spanner in the works.