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.
The
reasonOP_RETURN transactions are valid is to allow people to store data in the blockchain.
A specialized cryptocurrency could be created to store data like this (eg. altcoins such as storej) for this matter.
I think we both know such an altcoin would not give the same authority that the message is unchanged as bitcoin would.