The stupidest thing to do is to build mobile version of a website

Your post seems like troll-bait but I'll bite...

As a broad general statement, that's wrong. Let's say that your website is a combination of content (mostly static text and graphics) and web "apps" (forms, dashboards, interactive tools, etc). In most cases, your content can be device-neutral or (even better) mobile-first design. No separate mobile version needed.

However, it is likely your "apps" will suck when squeezed down to mobile size. The layout will be terrible and the interactions may be so broken as to be unusable. They'll work about as well as a king-sized bed and full-sized bathtub in a pleasure boat.

Better advice would be: Use bootstrap or some mobile-ready layout for your site's content and review your web apps on a case-by-case basis. Then, you very well might want to pay the fine young gentlemen or ladies who know mobile user-experience to rebuild some of those.

Are you retarded or something? It does NOT cost extra to build a mobile version ESPECIALLY if you use a framework like Twitter bootstrap from the get go.

Responsive is built in--and you don't need 2 versions just one version that scales both ways. You are correct it is stupid building two versions - but you can build 1 version that ACTS as two different layouts.