Your suggestion would collect lots of bogus email addresses and other bogus info. By issuing advance ticket to your email ensures collection of valid emails.
But the venue should be open to non-ticket holders as well and advertise that so people know.
Do you think that would be a problem? I must be naive. I can’t see being a Trump supporter, liking the president so much, standing in line for hours, but handing in false information.
In any case, not much good having a valid email that belongs to a ne’er-do-well leftist.