Purposely scratching in 8-ball?

[rowdyclassmate]

What happened was this: I had 2-3 balls left with no shot. My opponent had just the 8-ball left, but it was close to the rail on the other side of the table. Well within the mark where you cannot pass for ball in hand. So essentially, his only shot was shoot across the table (longways), hit one or more rails and pocket the 8-ball.

Now I've always played where you can purposely scratch... it's a defense move. Especially if you have no shot or an impossible shot leaving you in a bad position. He said it was illegal. Based on the additional information, what is your ruling? Legal or illegal?