picking up litter in your local park, or just volunteering to trim the weeds in it, does make a big impact.
the problem is once you start doing that don't hang around in the park looking for litterers who are trying to 'ruin' your good deeds.
i have notice in volunteer work there is a fine line between doing good, and then imposing your rules on everyone else and become massive asshole. this is why HOAs and such go so wrong. they usually start off with good-intentions but get warped into perverse controlling nonsense.
and if you volunteer and find out the people around you are weirdo assholes, just quit and do something else. i joined a community garden awhile back and left after 6 months because so many members were losers who were just shitting on everyone else's plot for not being as nice as theirs or getting jealous that a plot 10 ft over 'got more sun'. it was insane how petty and pathetic a lot of the long time gardeners were because they felt they were 'owned' the garden.