I don't think the issue is that the AI should stop proposing law changes (they actually didn't used to, and I filed a number of bug reports to try to get it fixed!), I think the issue is that sometimes the laws they propose don't really make sense.
One in particular I have noticed is a preference for Arena Combat over other types of Challenge when it doesn't really make sense. I've had Federations with Megacorps where the Megacorp will propose Arena Combat constantly, despite not even being a Militarist.
I think something funky is going on with the weights there, so that's the thing I think needs tweaking.
Honestly, if a Federation is having a constant, years-long disagreement about how things should be structured politically or administratively, it's going to cause strife and drop cohesion. That mechanic makes sense. The issue is that the AI should be reasonable about what they propose based on their ethics, civics and personality.