"Just saying." Or as Rev. Run (yes, formerly of RUN-DMC) likes to tweet, "Jus sayin'"
I quickly tired of this little colloquialism. "Just saying" reared its head in forums from Twitter to the publications of some of my favorite journalists. I've ascertained this phrase somewhat parallels IMHO (in my humble opinion). The spirit of usage is softening a sharp observation--"I'm merely stating what I observe, so what I see is not necessarily my problem, but I've got a problem with what I see." I think this opinion/observation disqualifier was spawned by a hyperbolic outrage culture that screams opinions. People still want to share their opinions and observations, but they don't want to look like jerks doing it. Therefore stick a "just saying" on the end somehow makes the observation uttered with a little more decorum. I think it falls flat. Just saying.
Consider the Southern U.S. cousin to "just saying," "bless his/her/their little heart(s)." They may not have the exact same function, but they both serve as opinion softening agents. Though the Southern version can be much more nasty, yet somewhat compassionate--(for example, "What a jerk. Bless his little heart.") the Southern version has had staying power, probably because of its charm. Though the phrase can be abused as a license to say anything you want about anything or anyone, there is also a spirit of recognizing the sinful potential of one's own tongue. "Just saying" has quickly become annoying. This phrase is well-intentioned, but the spirit of communication should be clear in tone and/or body language (more challenging online) without adding the phrase.