In general, I see no problem with law enforcement reading information someone posts publicly on social media and using it against them if it constitutes evidence of a crime or intent to commit a crime. I do, however see some issues with this.
One of them, not mentioned in the article is that the US government is demanding that visa applicants tell the government about all their social media accounts. Being forced to reveal a pseudonymous account is a privacy issue. In addition, the software is looking for '"derogatory" comments about the nation', which is a free speech issue.