I think the badness of the fallacy (or ‘fallacy’) depends on the surrounding context.
If, in a one-way communication, someone presents ‘X is an A’ as if nothing more needs to be said, that’s bad. Or if they’re engaged in a conversation but they present it as some kind of unanswerable knockdown argument and refuse to discuss it, ditto. (Especially so if they’re using it to smear the other side in the eyes of onlookers.)
But if it’s a proper conversation and they are engaging in good faith, it’s fine; the next step in the discussion can be to tease out which features of category membership are important in the present context, to what extent the entity in question has them, etc.
e.g.:
‘MLK was a criminal’
‘yeah, and normally that’s a bad thing, but in this case he broke unjust laws in ways that were necessary to serve a very important end’
‘I agree, but I still think we should be very reluctant to publicly celebrate criminality, lest we weaken the social foundations of respect for the law’
‘fair enough, <but I disagree in general, because.../and I agree, but here’s why this is an exceptional case...>’
I think the badness of the fallacy (or ‘fallacy’) depends on the surrounding context.
If, in a one-way communication, someone presents ‘X is an A’ as if nothing more needs to be said, that’s bad. Or if they’re engaged in a conversation but they present it as some kind of unanswerable knockdown argument and refuse to discuss it, ditto. (Especially so if they’re using it to smear the other side in the eyes of onlookers.)
But if it’s a proper conversation and they are engaging in good faith, it’s fine; the next step in the discussion can be to tease out which features of category membership are important in the present context, to what extent the entity in question has them, etc.
e.g.:
‘MLK was a criminal’
‘yeah, and normally that’s a bad thing, but in this case he broke unjust laws in ways that were necessary to serve a very important end’
‘I agree, but I still think we should be very reluctant to publicly celebrate criminality, lest we weaken the social foundations of respect for the law’
‘fair enough, <but I disagree in general, because.../and I agree, but here’s why this is an exceptional case...>’