I would say bashing is criticism without a good example.
'they are idiots and stupid'

Opinion would be with an example.
'I think X because I saw Y.'
Example:
'I think Egyptians are scary drivers because I live near Khalifa stadium and when Qatar played Egypt it was terrifying with the wreckless aggressiveness.'

'I think Indians are good football fans because although they don't know a lot about the game they cheered their team on even though they were losing'.