Say a philosopher has decided, all things considered, he is a nihilist. There is literally no meaning in the world, whatever we might want to call ‘the world’, there is no such thing as truth, there is no ethical right or wrong, there is no point to it all. What can we do about this? I think there is an argument for not even bothering to engage with him at all, along the lines of Pascal’s Wager.
If there is no meaning to anything, in a very strong sense, then if you are right, it doesn’t matter. There is no right or wrong anyway. But if you are wrong, then there are consequences to your being wrong, because there is some sort of meaning in the world, that you are failing to do justice to. So it would be sensible to not care about anyone who is a committed nihilist, philosophically, because if he is right, it is nothing to us (in the same way everything is nothing); but if he is wrong, well, there were more promising positions we could engage with anyway, and we only have a finite amount of time to do this in.