Saying something like this without context is stupid. If we're talking about smartphones, then I agree, more cores are stupid. I mean, 8 core CPUs in a phone? Even in big.LITTLE it's just too much. But on the desktop, and as long as we stay within reason, more cores make sense. It's not rare to see a desktop user doing multiple things at once, with some of them requiring multiple threads anyway. And I don't mean browsing the net while listening to music, but gaming while rendering or encoding/decoding or something like that. 8 cores/16 threads is as high as I would go for a consumer build with current software. It's by no means the sweet spot, but I would give the sweet spot award to 6 core CPUs, not to quad cores. Quad cores are ok now, but I suspect that that will change within the next few years. Not many things will require more than 4 cores, but if something actually uses 4 cores and 4 cores is all you have, I can't help but think that performance will take a dive, because there are also things running in the background.
But that's just my 2 cents. Also, I think sometimes Torvalds says stuff just to seem relevant. But I digress.