Really, they are just doing the supervillain thing of blaming the failure of their agenda of the heroes instead of themselves and their insistence on insane "solutions" instead of practical ones. Batman's not going to swoop in and stop Ra's from distributing birth control and sex education pamphlets.
It seems you've missed the point of their argument.
They aren't arguing that the JL is a boot on the neck of humanity forever.
Their argument is that as long as superheroes like the Justice League are running around, people will be too lazy to fix the big problems themselves.
Ozone layer gone? Why do something to fix that when you can just wait for "fix ozone layer man" to do the job for you?
So their claim is that humanity will never grow up as a species as long as humanity lets metahumanity change their collective diaper and pre-chew their food.
Necessity is the mother of invention.
As for actively opposing their plans, that's because their plans are supervillainous.
Ra's could solve world hunger and overpopulation in one go by asking Brain to come up with an easily produced food that covers all nutritional requirements, but lowers fertility, and deliver it for free to everyone in the world that can't afford normal food.
But no, it's death ray satellites and activating supervolcanoes and all that nonsense instead.
And that's when you give them the benefit of the doubt that their "caring for humanity" isn't just a thinly disguised excuse to gather power and money for themselves.
