I remember reading somewhere that George Takei accepted the role of Sulu only because Gene promised him that he wasn't going to play a "caricature" asian stereotype, which ended up being true.
I thought Takei "accepted" the role because he was a working actor and they offered to hire him.
If you'll notice, very few of Takei's roles during and after that time were rarely any sort of caricature stereotype (by contrast, any Asian with a thick accent or evil streak or someone like Mickey Rooney in Breakfast at Tiffany's were a dime-a-dozen during that time period). Takei in Mission: Impossible was a guest IMF agent who, kind of surprisingly, left the martial arts to the other heroes; he was a romantic interest to Mrs. Livingston in "The Courtship of Eddie's Father" (and these days, being a sympathetic Asian American romantic lead in film/tv is still a rarity). And during his college lecture circuit, Takei would emphasize the importance of taking on Asian roles that weren't racist caricatures simply because there were so few Asian roles to begin with, nevermind positive ones -- submit to one caricature and you and others like you get typecast, and stereotypes are enforced instead of proper media represenation that a larger audience so often takes for granted, which, in turn, limit the roles that casting directors would even consider for someone like Takei. So if you as an ethnic minority do get a positive role, you try to make sure that you play the HECK out of it as a character first and foremost. The possibilities of the audience's imagination is challenged, just like how TOS dared the audience to imagine a senior staff like Kirk's.
On a side note, and I realize that the show's famous for getting many distinguished Trek alumni, one reason why I dislike the Big Bang Theory is because Raj is often the target of just
so much microaggression from other characters, and when he complains, they handwave it and dismiss it, as if his experiences don't really count (unless, of course, it's a Raj-centric episode).