I'd say having false belief (believing oneself not to be smart, when in fact, one is smart) is more harm than good in the long run.

I answered this elsewhere, but... I think it is ideal to just exist without putting smartness on a scale. Smart is not an inherently good or bad thing IMO. It just is. What you do with "smart" matters, so we focus on doing and effort in my house, not on inherent capabilities. Also, maybe you as a person just don't want to do "smart" people jobs when you grow up? Probably you will, but if you are holding yourself to some standard it could set you up for years of unhappiness if you feel you are "wasting" your talents.

Being smart is inherently good. It is ridiculous to suggest otherwise.

You can't argue Hitler, Stalin, etc weren't smart in their own ways. So being smart is not inherently good, it depends on what it applies to. There could be smart pimp who makes a lot of money, does that make him good?

Maybe being good is inherently good?