The point is whether people have a 'reasonable expectation of privacy'. That's often interpreted to say that you're fine in a public space, because people have no 'reasonable expectation of privacy', but you'd probably face a challenge if you stood in a public space and photographed people walking in and out of an AA meeting.
Likewise, in a private venue, it's still possible to have 'no reasonable expectation of privacy', and gigs and pubs are an example. You need permission from the venue management, but that doesn't affect the 'reasonable expectation of privacy' that attendees might or might not have.
There's no one cover all, get out, it's always fine or always wrong. As
@Phil V points out, it's really at the point of publication that objections can become legal processes.
IANAL, personal view, free advice, etc., etc.