I think it's perfectly acceptable to challenge people with differing opinions, but if approaching a conversation with a predetermined objective to change someone's mind, the outcome will generally be disappointing.
Discussion
I don't like the modern usage of "opinions" – it implies a certain impulsivity that doesn't require thought. But most actual opinions aren't random: someone likes something or someone based on an informal analysis of their experiences. Some experiences we interpret correctly, some we misunderstand. Some misunderstandings are accidental, while others were intentional. Finally, some intentional misunderstandings are to help us, and others are to deceive and defraud.
It is these intentional deceptions that are the most corrosive. Opinions that rest on them will be backwards, acting against the best interests of those who hold them. I may agree or disagree with someone's philosophy, but when they can't see that they have built a castle on the sand, what else can be said?