Usually an "Oh, hm" sort of reaction. Or if it's something he likes, sometimes an, "Oh, why not?" requesting more information and reasons from me. So far I haven't felt him trying to pressure me away from an opinion or even really require an airtight reason. In fact, sometimes it's like he simply takes it and incorporates it into how he interacts with me.
Here's a hopefully helpful albeit rather basic example: He knows I don't enjoy very spicy foods and he even knows approximately my cutoff point for spiciness. One time we all were at a restaurant and I said I was planning on getting a particular dish, one that was new to me. He interrupted a small-talk conversation I was having with someone else and said, "Have you had [ingredient] before?" I said, "No." He kind of made a
face so I said, "Why?" He kept making the
face and looked to be searching for words so I guessed, "Is it spicy?" He replied, "Yes, you might not like it." I thanked him and chose something else. Someone else got something with the same ingredient and let me have a taste; it wasn't over-the-top spicy but I was glad to not have it as my whole meal.
So that's what I consider one reaction to a negative opinion of mine. It's like he filed my preference away as practically applicable fact, and then felt concern that I stay unbothered by whatever it was that I didn't like to the point where he'd insert himself into the situation to prevent it.
Granted, that's something sensing-based. As far as moral opinions or boundaries that I don't feel like crossing, so far he seems to have a same sort of "taking into account" approach.
For example, he likes to explore and sometimes that (apparently) involves going through "do not enter" doors or through boundaries that many would consider "do not cross" requests. I, on the other hand, have almost always been a rule-following individual since childhood. So unless I have a compelling, even moral reason to flout others' boundaries, I usually stick to what I "should" be doing. The exception might be if I sense that the rules in a particular context are flexible anyway, e.g. driving the speed of traffic instead of strictly the posted limits. For me, it's respecting others' wishes, which is something I would like done for myself.
Anyway, that's a difference between us, and he seems to treat that preference of mine (and those of others) similarly to the food one. He'll suggest, say, "Let's see what's over here" or "Do you want to check this out?" but when I've hesitated he doesn't push and then seems to assume that henceforth we'll avoid whatever it was. (He doesn't know me well enough to know that sometimes I just need to ruminate on an idea for awhile, then be comfortable with trying it.)