Should a persons susceptibility to fasicsm be identified?

Well, one context I'm already familiar with is the counter-terrorism duty in the UK. There is a program called Prevent that is designed to tackle radicalisation risk that could result in terrorism or non-violent extremism.

These programs basically work by placing a duty on certain types of organisation to report concerning behaviours that could result in radicalisation. An example would be a teacher or social worker overhearing a teenager espousing violent ideological positions that they'd been exposed to online.

This then results in a referral to the local counter-terrorism police unit, who carry out an assessment to determine the level of vulnerability and risk. Far-right ideologies including fascism can be accounted for here. Depending on the outcome, this may result in the referral being closed, or a multi-agency support plan being developed for the individual.

In that narrow band of circumstances, determining someone's susceptibility to fascism as an extremist ideology is warranted. That's in the context of a reactive specialist law enforcement assessment, when there is a justifiable national security interest in the prevention of terrorism.

That said, this is very different to indiscriminate profiling on a population level. If everyone in the UK was subject to mandatory fascism assessments, that would be massively intrusive and disproportionate, and an enormous infringement of civil liberties - even if the government attempted to justify it on the same national security basis described above.