Ask HN: Is it foolish to open source your SAAS business source code?

Say you come up with some great productivity application. It's web based, has a back end and a JavaScript front end for browsers and mobile. You put it on github under an MIT or BSD or similar license. So corporations or anyone else can download and install your software and use it at no cost. On your main website, you offer the software but on a per-user fully hosted, running online basis. So your revenue will come from people signing up to use your fully hosted service where they don't need to make any effort to install or configure - it just works. You also make money offering support contracts to people who have downloaded and installed their own copies of the software. The reason you have open sourced it is to spread the word, gather interest and build community around your product. The theory being that the vast number of free users will be the impetus that leads to a small number of paying people discovering and using your product. Maybe free and open source is more ne