I'm so glad to have come across this conversation! :)

I'm studying to be a high-school teacher and I googled this term after a good friend of mine said (after a few beers), "Look at the facts. Nobody respects teachers anymore. I know you're enthusiastic and all, but you'd be mad to think that your profession has the credibility you'd like it to. You'll be burnt out after 5 years. JUST SAYIN'"

Now, I'd always loathed the phrase (used postpositively) even before this exchange, but this just reinforced my reasons for doing so. It assumes the right to say something without the responsibility of having to be held to account for it.

Besides, what is it to 'just say' something anyway? When you 'say' anything, you lose control of its meaning, inferences etc the moment it leaves your mouth and reaches the ears of your listeners. Most of the time, your listeners will largely understand the phrase as you meant it. However, this is often not the case, and when this happens it's the responsibility of the speaker to further clarify/justify his/her statement - that is, if you want to avoid offence or confusion.

It seems to me that 'just sayin' absolves the speaker from any responsibility to provide such a follow-up. So far as I can see, this can only mean that the speaker is unwilling or unable to explain or justify what was just said. Personally, I think you should keep your mouth shut in this case.

Ah, this was so cathartic :)