I get the impression that the OP wants to store a message that he can prove is unchanged. There is nothing stopping an operator of a website from changing content, or back dating a blog post.
That still doesn't justify storing any random messages in bitcoin's blockchain though. A specialized cryptocurrency could be created to store data like this (eg. altcoins such as storej) for this matter. You never go to your bank and tell the clerk you want to deposit a bag of potatos in your bank account!