“I’m just saying”

In 1826 it occurs in print here:
Hearings Before Subcommittee No. 3 of TheCommittee on the Judiciary, House of Representatives, Eighty-first Congress,

as "I'm just saying that this is ridiculous and unfair".

As a stand-alone sentence, possibly about 1936.

This is a phrase I've often seen in comment sections of blogs and videos. Those comment sections frequently degenerate into hothouses of abuse, in which a poster is likely to receive a venomous reply. I imagine that by concluding a comment with "I'm just saying" anticipates such a response and attempts to allay it. Which is to say, the phrase may be used to try to soften remarks that might be construed as criticism.