One might ask if there is an expectation of truth from each and every user of Facebook. The practical answer is no. That is, unless billions of posts could be tested for veracity. Good Luck with that. However, be careful of the harm or injury caused to persons or interference with the rights of lawful businesses.
Before you write, even if it’s the truth, remember that attorneys are expensive. Depending on where you live, the State/country might be, not your protector, but your most ardent, diligent persecutor. Truth can get expensive fast.
Repeatedly drilled into me was the maxim, speak the truth and speak it ever, cost what it will. That helps with building character in a child; respect for virtues. Later, I discovered, it depends. The situational context might dictate. Both lies and truth might be hazardous to one’s life, consequential to reputation and worrisome to the wallet. But, I will stop here, lest I enter that murky, dangerous, space of Kellyanne Conway’s, “alternative facts” and forced to use a plural form.
Iconic writer, Mark Twain, advised: “Where a thing is a widely accepted truth, it might be best to let rest.” Please see the report on the link.