It could be some sort of pride driving them as well. Being wrong is wounding their pride and they get angry. Or maybe they just don't like being questioned, maybe they want you to be the obedient, non-questioning child. If so, you might never get anywhere with them. It could also be you come off a certain way to them which they find unpleasant. Difficult to say without seeing you interact.
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As for topic, I usually don't offer much of own opinions to people outside friends (and forums, I guess). My interaction with my family is mostly various small talk of no importance. I'm fairly different from my family, sometimes it's as if we're of a different culture. So for me I see them as having their priorities and opinions, and me mine. There's no reason to really exchange them. I wont say this is necessarily a good or the right way to interact with people, though.
So I'm generally not considered negative by my family afaik. I usually remain quiet and talk little. And what I say is generally trivial. Recently I was visiting some family, grandparents, aunt and I said some retarded things which later I figured I should've kept to myself. But my mother told me later in private she thought it had been a very nice evening and it was nice hearing me talk. That kinda took me off guard.
I guess I'm also fairly aware of what people "want" from me in a conversation, and since they usually get that they will be biased to think well of me should I ever need to address something "negative". In workplace, my suggestions for changing things that didn't work was more considered enthusiasm and interest rather than pessimism. I can come across as a fairly upbeat, positive person if I want. One of the perks of being ENFP, I guess (yeah I noticed thread was in the INTP section). Though I think this ability has diminished as I've become more cynical and distanced.
Anyways. Tldr I only offer the "negative" if I think it's important to point out or if serves some purpose. Most of the time I leave people to their business regardless of what I think of their doings.