“Cautious is just a _________ for being scared.”
“Opportunistic is just a _________ for being inconsiderate.”
“Not too bright is just a _________ for being dumb.”
“Simple is just a _________ for being ignorant.
The word is used often in politics to expose someone as being partial to a particular idea or identity. The word in question has a similar nature to the word “pseudonym”.
I think the word you want is euphemism. According to Merriam-Webster,
euphemism – noun
- The substitution of an agreeable or inoffensive expression for one that may offend or suggest something unpleasant
- The expression so substituted
It fits all your examples, e.g. “Cautious is just a euphemism for being scared.”