Perhaps, but they cannot violate people's rights in doing so.
Is this just your opinion, or do you have concrete evidence to back it up? Argument from incredulity is a logical fallacy.
The Secret Service can, of course, take preemptive action. But there still needs to be a credible threat, and potential heckling or exposure to differing opinions are not credible threats. Th
e full extent of the Secret Service's powers and authorities is laid out in law here:
https://codes.findlaw.com/us/title-18-crimes-and-criminal-procedure/18-usc-sect-3056/
This is a Public Affairs guidance document for the Secret Service, as an example of their usual policies and procedures:
https://www.governmentattic.org/45docs/USSSpubAffairsGuid_2017-2020.pdf
Of particular note:
View attachment 381377
View attachment 381378
It seems pretty clear that USSS SOP is (or at least used to be as recently as 2020) to only step in if there is a
threat against their protectee(s).
"Privilege," in this context, is a very vague term. Yes, it is a privilege - but the privilege is conditioned on compliance with the rules of the event, not the potential that the VP's fee-fees might get hurt. Either way though, the right being violated here is not a right to access an event, but rather McGonigle's First Amendment right to free speech. She registered for a public, government-funded event, complied with all rules of said event, and was denied access based solely on her speech - in other words, she is being punished by a government entity for speech, which is something expressly forbidden by the First Amendment.
The closest example of a similar event that I can find reference to is
"Plaid Shirt Guy", who was kicked out of a Trump rally in 2018 for making incredulous faces as Trump spoke. The differences being that:
1. This was, as far as I can tell, not a government-funded event.
2. He was kicked out for his actual actions during the event.
3. The rally's organizers (not the government or government officials) had him removed.