The theory that vaccinated people are less careful with socialization and pay less attention to symptoms is the exact same argument being made about masks. This makes agreeing or disagreeing with the theory a bit socially complex.

If we agree that protections like vaccinations and masks do effect people to behave more risky, then the benefit of masks need to be balanced towards that negative effect.

If we disagree that protections like vaccinations and masks do effect people to behave more risky, then the benefit of vaccinations need to be questioned.

Either way we are questioning the effectiveness of masks and vaccinations, two topics which is quite controversial to question.

Wow, that "people wearing masks will party like it's 2019" hypothesis is an interesting specimen: to me, almost two years into the pandemic it seems almost absurd, because when I put on a mask I'm immediately "pandemic me", with all the routine precautionary behavior patterns. I can only switch that off without a mask. But back in early 2020, those connections were not set up yet, it would have been quite likely that wearing a mask would have got the precaution box checked, leaving everything else "2019". At what point has it changed? Has it changed for everyone?

To me, putting on a mask is acknowledging of a high risk environment, like using a mass transportation during a pandemic. Airborne virus spread fast in crowded environment with limited ventilation, and if one has to be in such environment then doing anything to limit spread is good. The problem is when people started to use masks in order to allow themselves to be in an high risk environments.

For my perspective here in Sweden, not much has changed from last time during the holidays and this year. People still seem to want something to allow them go into high risk environment, like Christmas parties, weddings, mass transportation travel, and shopping during rush hours. To me it the same people who went to those last year with masks that goes to those things this year with vaccines. Thankfully vaccines is at least more effective and thus the outcome seem less worse this year for the health care system.

that is probably because the first to be vaccinated are the old, weak or diseased people and the unvaccinated are children with strong immune systems.

It's a rubbish assumption though. According to the UK data (which is age stratified), unvaccinated children get infected much more often. You could say that children have strong immune systems therefore they don't get sick but only infected. Maybe vaccination for children further improves their immunity that they don't get infected either (will see if it works for omicron though). As for other people, even vaccinated easily get infected but the severity of illness is reduced.