I think the versatility of IS outweighs any IQ-loss.
That is...provided that you need IS. Some people don't.
Ah, but that is debatable.
Photography is about statistics; keeper rates of images without shake blur are no guarantees. If you take enough shots, you will get a blur free image at 400 mm and 1/60 s at some point in time, after many tries. However, with IS, you are almost guaranteed to get those shots.
And because it is about statistics, even at fast shutterspeeds IS helps...
Kind regards, Wim