This is wrong in an important way (that's quite relevant to message boards like this one, about which you'll often hear that arguing about controversial subjects is pointless because nobody ever changes their mind). Basically, nobody ever individually changes their mind in the moment, so it appears as though debates are ineffectual. But that's only because people change their minds slowly, in private, in response to thousands of inputs.

And it might not even be the person you're talking to who eventually changes their mind. It might just be a reader, a thousand of whom exist for every one person visibly contributing.

You can't see the mind changing, but it's wrong to conclude that therefore it never happens.