[raymondduke]

First, you ask if he wants your honest opinion. No one likes unsolicited critism.

Second, what makes you qualified to say his idea sucks? Many people in history were told their idea sucked.

Next...sometimes it's good to let people fail. It builds character. We learn by making mistakes.

But if you feel like you must give criticism...don't simply say it sucks. That's just as useless as saying it's wonderful. If you don't like his idea, say what you don't like about it AND give a suggestion about how to make it better.

The bottom line: your opinion is just one of many and a suggestion is always better than a criticism. Especially when he's your friend.