I dun think so, cos every citizen has a constitutional right to profess, practice, or propagate his or her religious belief, so long as such activities do not breach any other laws relating to public order, public health, or morality. However, negative portrayals of religion are subject to censorship. We need to be 'tolerant' and not 'aggressive'. Just try not to cross the line, that's Singapore, like it or not.
In Singapore, we have Respect-based on fear, therefore religion is a touchy topic, kind of sucks uh..?
Well, Singapore, as you probably already know, is a very conservative country as it is. Religious discussions are always kept to a minimum, if not non-existent. When you say "opinions", what kind exactly? It does depend upon the nature of what is to be voiced.
Personally, I see atheistic arguments as a 'lesser evil' than a religious person preaching sedatiously against other religions. The latter is certainly chargable in Singapore from the recent case where a Christian couple was persecuted for distribution of pamphlets that negatively potrayed other religion(s).
Blogs may be more glaring because it is written by the owner and may be perceived as more harmful. It is commonplace to see atheists arguments in several publicly-viewable forums though.