Up until fairly recently I played in a resort area known as a place where celebrities, very wealthy people, and very powerful people go to relax and/or play without the usual public attentions that come with fame. We'd do shows either at someone's vacation home (well, estate really) or at a venue closed down to host the event. It was not uncommon for us to go through a security screening including vehicle and gear search, to have to give up our phones, and for direct interaction to be forbidden. Also no social media about the event allowed before or after.
The difference is that in our case these conditions were presented up front and were written into the contract. It was our choice to agree or not. I think if I showed up at a gig and they were sprung at the entry point I'd back out. That would make me wonder about safety. Yeah, I'm old enough to remember back when every gig was at a place that had just the one phone behind the bar and a pay phone out front, but cell phones have made me soft.
Funny aside: at some of these events during setup we were specifically told that if Mr. X (loud male who used to be a big star) wanted to sing a song we absolutely had to allow it. If Mr. X wanted to sing a second song we were supposed to take a tuning break and wait for staff to lure him off the stage.