Disregard, dismiss, discount. I'd go for the first.
But you might perhaps be looking for gaslight.
to psychologically manipulate (a person) usually over an extended
period of time so that the victim questions the validity of their own
thoughts, perception of reality, or memories and experiences
confusion, loss of confidence and self-esteem, and doubts concerning
their own emotional or mental stability :
In your examples, I feel there's a progression - I wouldn't use the same verb for all three {but see the disclaimer at the end!}:
"Well, that's one opinion,"
this is dismissing an opinion (you think this, it's OK, I just don't care or don't want to go to war on it)
"I understand that's how you feel,"
this applies a bit more pressure on the recipient, maybe beggaring the question of why they feel like this and hinting at some problem (ignorance, or worse) - I'd say they patronize.
"That's OK, you'll understand someday."
this is even worse, as it not only dismisses the other's opinion, but actively implies that it's wrong, and its holder can't understand this just now. Also, holding the wrong opinion is "OK", which means the owner's beliefs are just irrelevant. That's disregarding, or worse.
The next logical step would be gaslighting - something to the tune of "well, of course we all know why you would believe that", actively crossing from patronizing to saying openly that the other has some sort of problem.
(Note that I'm translating to and from my mother tongue, which isn't English, and the choice is in great part a matter of feeling. Actually, choosing the verb colors the description, attributing a more and more evil intent on the speaker: a dismisser is aloof, distracted, maybe already determined otherwise and possibly for good reason; maybe they are motivated by civility, and trying to not quarrel. A disregarder is at least a bit disrespectful. A gaslighter is a manipulator).