Language vs dialect damaging? Sure, there are problematic definitions, but the conventional linguistics definition based on mutual intelligibility is useful, if a bit fuzzy.

linguisten:

True. 

But: in many highly standardized official languages, “deviations” like dialects are frowned upon and considered less pure, less elaborate, or less refined, even deficient. Thus, speakers of dialects are in far too many cases still perceived or even brandmarked as less intelligent etc. That is the danger.