Opinion usually has something to do with level of knowledge, and the level of knowledge can actually always improve. Probably it is rather the rule, than the exception, that opinion changes, if knowledge rises. The further one looks into the past (be it the personal one or the one of mankind) the rarer become there, to all appearances, the exceptions.
So what is there to give on opinion? – Probably not too much.
If one then still considers, how much opinion upsets, and not only emotional energy requires, which then cannot be used any more to extend knowledge (by arguing, for example, instead of asking), I can’t help but think: One should leave opinion be, where it is only possible. And when it is not possible – because sometimes you need an opinion – it is hopefully wiser, when you have not wasted so much energy to have an opinion about everything.