A US-born NASA scientist was detained at the border until he unlocked his phone
Their point about how other countries will take the US's stance as a cue is somewhat scary.If you try and cross any border it will be relinquishing access to all accounts.I'm assuming email also comes along with 'social media', since communication is by its definition social.So how do you protect yourself? 
I think just going with "Don't have any social media" isn't a good answer because the relationship that children growing up today with the internet is almost completely different to even people 10-15 years older than them.Someone having carte blanche access to a person's phone will find something if they want to.Imagine you're in a few group chats, someone mentions doing some drug. And you've just entered a country where that's an instant prison sentence.Maybe some off colour jokes about politicians? Proof to kick you out or at least detain.I imagine we're at the cusp of something much more unsettling. The technology to reverse image search a face is available today. It's pretty easy to make you appear associated with anything, anyone, etc.