People seem to think social media is akin to private communications where it's more akin to the public square. Making your IG/FB/whatever profile private doesn't change that.
In NYC for example, there's been a large uptick in teen shootings, many adjacent to schools, and a lot of it involves the idiots posting on social media before & after. One tool could be simply scraping social media for these postings. Another alternate, pre-internet tool was stop&frisk.
While you have a constitutional right to not be searched without consent/probably cause, you do not have a constitutional right to spouting off in the public square without consequence. What you say publicly can & will be used against you in the court of law.
Putting out an IG post of yourself with illegal guns or inciting a shooting is no more private than printing out posters of the same and putting them up around the neighborhood.
Actually, in the U.S., you literally have that specific constitutional right.
The First Amendment protects "spouting off in the public square without consequence" via the Freedoms of Assembly (the right to gather), Speech (say what you like without consequence), Religion (believe what you like), and the right to petition the government.
Loud complaining or even vague and non-specific threats (such as "I'll make you pay for this!") are actually protected by the First Amendment.
There are very rare and limited exceptions, such as "directed to inciting or producing imminent lawless action and is likely to incite or produce such action".
It seems like the OP might have been conflating free speech with admissions of guilt for other crimes, but "spouting off" is not, and must never be, a crime.
By my reading, it wasn’t OP who did this conflating.
"spouting off..used against you in a court of law"
But, even if the OP didn't intend for these two to be tied together in this way, then a very strong constitutional right still exists for spouting off, so whether conflation occurred or not is moot.