Definitely praise them on Facebook & Trip advisor!
I have been around vegetarians all my life and don't find them too difficult to accommodate.
I do agree that having a lot of people around with allergies can be annoying, but I am not sure what we are supposed to do!
I, like many of my generation was brought up to eat what was put in front of me and 'not make a fuss'. I am not at all a fussy eater, but over the last 30 years or so have gradually developed a few food allergies / sensitivities that do make me unwell - not life-threatening but 2-3 days of discomfort.
I do tell people when I am invited out, and always feel very apologetic. The alternative is to decline invitations which seems ridiculous!
I enjoy cooking, and so does DH so we are happy to cater for various 'food issues' when we invite folk to us, but I do see why it can be a faff.