1) You don't know anything about the topic i.e. you have not read even some basic papers/articles/books on the topic, do not blog.
2) You have put some effort reading about the topic, have understood something but a lot still remains to be read and understood. Blog, but make sure to let people know your depth so that they are not dismissive of you. You are trying to elicit some good discussions and receive feedback from people who know the subject better than you, which is a great help in planning your further studies and can short-circuit your learning curve. This is called "casting a brick to attract jade" in the Chinese work "Thirty-Six Stratagems".
3) You know the subject very well; Blog with a clear preface note as to whether it is intended for beginners/intermediates/experts in the field.
Finally, please do not be superficial/obvious, try to give as many references as you can and also your motivation for what led you to think on the lines of the post.