So you would just brand yourself as proven liar - and end up having an even higher risk of being rejected at the border.
You see where this is going. If you use social media, you will have to state the truth. And you know where that leads to.
Which are all captured by Prism and other mass surveillance programs (google "Edward Snowden").
Nobody escapes the NSA.
Which will simply be filtered out. Technology does not just evolve linearly.
These were the last words of the database admin before he went stark raving mad...
But seriously "filtering out" is a goddamnd hard problem, if the dimensionality of your problem space is high enough. You are talking about filtering out sockpuppets like if they have a tcp-flag on it. Even the best trained Neural Network can only work as good as the input-training parameters, and classifying large texts in natural language is still one of hardest problems (even for humans).
Yes there are, eventually you need to make a decision about whether to let this person into the country
Data (even encrypted data) is being collected and stored today. It is decrypted/made sense of whenever technology has reached the required maturity. At that moment, we become 100% open books. And you may feel that at the border (or elsewhere).
I thought they had info about the boston bomber, 9/11 hijackers, and san bernadino shooter, but didn't act on it because it was lost in the noise?