Harm - hurtful or bad consequences following an action.
Less - the lack of.
This word technically has quite a positive meaning. Something is harmless. It doesn't cause hurt. It has no negative consequences.
But I've yet to hear it used with a positive connotation. It's the sort of word that's tossed away with a tiny sneer. "It's pretty harmless" can mean anything: unimportant, useless, silly, inconsequential. At best, it won't hurt you.
If we say someone is harmless, we are usually describing people with low social status or value (children, old ladies, the village idiot). It's an insult to be called harmless. It means you are passive and undervalued.
The subtext of all of this? Simply not causing harm is not enough to be considered good. Passivity is better than intent to hurt, but it's not a positive thing in itself.