That's quite the sweeping dismissal of Kickstarter.

Well Jason Cohen wasn't talking in the abstract, he's talked about how he got checks up front before starting WP-Engine.

Obviously it depends on your exit strategy. Do you want to (a) get a loss making but huge user base or (b) bootstrap a business that has cashflows from day 1?

Sounds like that advice applies more to the latter route than the former.

Note the careful wording: "before you even start coding it". Coding is a time-consuming thing, very fragile (if you get it wrong, you may almost need to start over again) and brittle (making changes is, connectedly, hard). Very significant validation can be done without ever writing code. (That's a lesson that I've been learning this year, as one who delights greatly in coding.)