Let me start by saying that there are a few different groups of thought surrounding conversion forms as gateways to content like Ebooks, webinars, etc.
There are literally successful folks on both sides of the fence. And I mean really successful folks.
Guys like David Meerman Scott preach very heavily against having visitors fill out a form to download content. According to David, you should let your content go freely as it increases downloads and sharing - among other things. And it works for him. BIGTIME.
I don’t think I’ve ever been forced to fill out a form to grab something from Godin either. Although, I don’t remember the last time I saw content from him aside from an actual book or blog.
In their book “Content Rules,” Ann Hadley and CC Chapman mention that it is important to use conversion forms with caution, whereas Hubspot (and probably most of their partners) are 100% conversion form city. I don’t think I’ve seen anything from Hubspot that mentions NOT using a conversion form. In all fairness though - they will admit to benefits of both approaches.