It is not. Tax evasion is an actual crime. The IRS using public signals from social media to determine if somebody is cheating on their taxes is not the same as the NSA tracking your GPS location via your cell phone at all times.
You are correct. Perhaps I did not make my point clear. If you publicly post pictures of your new Porsche and your newly remodeled kitchen and claim that you only made $10k last year, why should that not be cause for the IRS to take a deeper look? You do not, by definition, have any expectation of privacy in that scenario. If you sent the picture of your new ride in a private message, that is a different story.
