Turning the tables on critical trolls

How to deal with the colleague/board member/voter who is quick to criticize whatever you're proposing?

It can't work/it's been done before/it's never been done before/you can't do it/we don't have the time/money/skills...

So easy to be right when everyone else is wrong, so easy to be confident when someone else is putting themselves on the line.

I start with this: do we agree that there's a problem? An opportunity?

Do we agree that we need to take action, that something needs to be done...