What’s the correct adjective to describe something that has the ability to make someone feel bad about themselves or lose their confidence?
If something is disheartening, it makes you feel disappointed and less confident or less hopeful. -- Collins
If something is demoralizing, it makes you lose so much confidence in what you are doing that you want to give up. -- Collins
If something just has the ability to make you feel bad or lose confidence, you may want to qualify these words by saying "potentially disheartening" or "potentially demoralizing".