I think all life deserves respect, down to the smallest possible insect.
The simple fact is that all life dies. How and when are the only variables. That one mosquito/dragonfly larvae/etc. makes little difference. They are a predatory species. They can reek havoc on your little aquarium/pond/house/etc. They may carry diseases. If you let it go it will breed. These may reinfect whatever ecosystem you don't want them in. These are far from endangered. If they weren't I'd say keep them alive if possible. but they are not. I realize this will make me some enemies/people who dislike me but you should kill them. I hold this aspect for most types of life. up to the "highest" life form, humans. We are a species that ruins environments and have overpopulated earth. Survival of the fittest baby. you are fitter and it is not endangered so smash the little buggers.
Just my two cents.
, as pea-brain suggested, does not resolve anything, in addition to being highly unethical. It seems that ethics and compassion are not fashionable nowadays.... That's a very closed-minded, backward way of thinking if you ask me. 
Not to go nutz on this, but we need to look at the big picture. Loads of these critters are naturarlized and not native at all. 
