You don't have to surrender the pen, you just don't go into the venue. I carry a pocketknife, I know enough not to carry it anywhere where I would be frisked.
It's my belief that you're being intentionally obtuse to be contrarian. In your example, what if you were carrying a small pocketknife that you've carried (legally) for decades and are told is not accepted at the museum for which you've paid in advance to see a special exhibit? Your choice is to sacrifice the sentimental knife or toss the ticket in the garbage. Do you see my point?
We can't have malls, retailers, sporting venues, concert halls, theaters, and restaurants just randomly deciding what they think is permitted and what isn't permitted.
~ Blue Jays ~