I thought this same thing. Hard forks probably do carry an inherent negative impact on a coin's value. But depending on the reason for the fork that impact could easily be overshadowed by a positive response. I think this factor is coin/situation dependent.
I do not agree it is inherently negative. In fact a coin where developers are unable make important changes (including hard forks) for whatever competence, organizational, or political reasons could see its value decline for that reason.
So I agree what what you said about it being coin/situation dependent.
Hard forks done for bad reasons or which are poorly executed will hurt a coin value.