Right here we have proof that McCallum was saying he didn't think Jar-Jar would work and he questioned Lucas about his use of the goofy Gungan, but George explained to him that his point was to be annoying to adults.
Rob Coleman did an interview where he said he "begged" Lucas to allow him to tone down the Gugnan's antics, but Lucas refused.
It's not that nobody questions him, it's just in the end, Lucas gets what Lucas wants. Which with the exception of portions of ANH has always been the case.
I don't mean to take anything away from Kurtz's obvious contribution to these films, but he was against Lucas making Vader Luke’s' father. I know some here would agree with him, but does anyone refute that most people loved the "I am your father" moment?
So this idea that Lucas should listen to everyone else when they are telling him his ideas are crazy is crazy in and of itself. For better or worse Lucas is the artist and therefore he gets to make the final decision. He can't just let everyone around him tell him how the movie should turn out, he has to keep a consistent vision for it, otherwise, you have too many chefs spoiling the stew.
Lucas has been enjoying absolute power since ESB. That didn't stop him from deciding Kershner and Harrison were right about the "I know" line. That didn't stop him from deciding the original cut of Empire worked better than the cut he tried to make. In the end Lucas does listen to others, but only when he agrees with them.
Yes, he did purposely design a character that less tolerant people would hate with a passion. It's an exercise in tolerance for the audience, and kids that learn how to tolerate Jar-Jar will in all likelihood be cooler to their fellow man as they get older because they won't be so quick to hate things they don't understand or find annoying right away. A lot of them will have learned Lucas' lesson about compassion. Just as a lot of us learned not to be so quick to anger from the originals.
The reason I say the people who didn't agree with him didn't matter is because despite critics and -some- fans crucifying Lucas and TPM over Jar-Jar, it went on to claim 2nd highest worldwide box office gross (at the time). So even with that ridiculous amount of hate, no matter how hard the critics tried to kill TPM at the box office (remember the ones that broke their word to wait until opening day to publish their reviews?), they couldn't do it. TPM not only survived, but it was the 2nd highest success at the box office up until that point.
I know a lot of you think Lucas isn't the same guy he used to be, but I say he's still a whole lot closer than any of us are.