Making Blot's source code public means Blot is more appealing to technical people. More importantly 'open-source' implies an insouciance towards money which I like.
It is not financially sensible for me to make Blot's source code available freely under the most permissive license possible. However, I'm determined to not sell Blot, ever. Releasing the source code has the benefit of increasing the value of the hosted service to potential customers while reducing the value of Blot if I were to attempt to sell it in a moment of weakness.
Intellectual property as a legal regime has its costs and its benefits. While ideas are inherently free, there can be advantages to establishing legal structures for their protection. However, I think the legal structures we've established to protect intellectual property are overextended. They often restrict rather than encourage creative endeavors.
I also like the spectacle of open-source. Work on Blot is done in public. I suspect it's reassuring to potential customers to see my git commit messages neatly formatted on the news page, for them to know that Blot is alive.
I like the ideals of the free software movement and I like Richard Stallman. However, I think the free part of Stallman's term free software is confusing. I'm also aware of the politics of the term 'open source', so I avoid both and when I address this topic on Blot's website I say that Blot's source code is dedicated to the public domain.