If one accepts that Bart is fundamentally
nihilistic then maybe - but then, as a 'child' wouldn't that be expected - at least to a degree?
If so, then Lisa counterpoints with more enlightenment, idealism - and [occasionally] refreshing cynicism. Homer and Marge represent their 'role' models, respectively. Maggie, perhaps more of a blank canvas, exhibits both - sometimes in unexpected ways.
If we believe the Simpsons is an allegory for contempory American society (and not just America and I'm not saying I do), and we're comfortable with that then Bart Simpson's behaviour is
justified if only because contemporary America has deemed it so. If we don't
then perhaps he's just a character in a satirical cartoon show. Personally I think it's somewhere in between.
It's amusing perhaps because it hits close to home. It forces us to laugh at some aspects of our own nature we may not otherwise be comfortable with, were they subject to more 'objective' scrutiny.
If [many] people didn't [even on a subconcious level] aspire to emulate some of Bart/Homer's disregard for convention then it would have no resonance. The same could be said of Lisa/Marge's aim to 'do the right thing'. Perhaps Mr. Burns represents some derivative of an Orwellian state ... and so on!
Homer's behaviour is excused because he's [portrayed as] an idiot, Bart because he's a nihilistic child who emulates his Father. Marge because she's [portrayed as] intelligent but frustrated with many aspects of her life, perhaps rueing some of the choices she made along the way. Lisa because she's an idealistic child who emulates her Mother.
It also occurs to me that blaming
politicians and legislation (while certainly a factor) is a convenient vehicle to avoid individual responsibility for what we collectively dislike about contempory society. After all, it's much rarer to heap praise on official organs for the things we do
like, isn't it we tend to reserve that accolade unto ourselves, so one might ask ... why is that?
I'm just playing here so please don't read the above as a serious
attempt to answer your question, that would require more than a few sentences on the Interweb.
I have yet to eat breakfast so my few functioning synapses may be playing tricks on me.