After reading this blog post about blogging Sinhala, I felt like writing my thoughts about the topic.
There are very few "yes" or "no" answers in life, so I don't think it is correct to rule "blogging in Sinhala is a good idea" or vice versa. Most answers can begin with an "it depends", and I think it is true here, too.
In certain circumstances, using in English on the Web is a good idea. When addressing a global audience, or selling to a product on the Web to the global market, not using English will definitely not serve the purpose.
A key argument for using Sinhala is about addressing certain audiences who are not fluent in other languages.
I think there is a more important reason. Certain things can only be done in Sinhala, and this argument holds for any other language.
A blog post is not always a piece of information to be transmitted to a maximum audience. Sometimes it is a work of art. Works of art are diverse, and this diversity is not only limited to language.
Sinhala is not only a communication medium. It also has a very rich literature: poetry, writings and what not. Being a living language, new Sinhala literature is made every day. And if Web is the medium for such literature, obviously, Sinhala has to be the language.
Check out this blog post for example. (You may need to enable Unicode support). It is a collection of Sinhala poetry from an online "hitiwana kavi maduwa", where people used poetry to communicate. I am sure there are lots of readers who appreciate such work. I can hardly imagine how such a blog post can be in English.
So I think the answer to most questions of life applies here as well: it depends. ;-)