I started using Linux as a better and free system than win95, and only after a while thought about the bigger software freedom issues. Before linux, microsoft was just a random company for me. I am not alone in this respect. And look how far open source has come.
In the same way, straw banning can be a 'gateway drug' to environmental awareness. You've done your bit. So you acknowledged there was something to do. Then you dont want that small bit to be meaningless, so you do a tiny bit more All the while advocating to other people this is a worthy cause. Then you find how bigcorps are flagrantly violating the good cause. Of course this cant be right. And drip by drip you wear down a mountain.
Try swapping out the 'wrong' and 'good' with something else and the reasoning seems far clearer.
"Hey, I've done my two hours of volunteering at the orphanage, now let me go back to running my child sweat shop."
If you feel the scaling is unequal, change it. At any scaling I can imagine the initial reaction to someone seriously holding that view is disbelief and then mocking.
Keeping everything else the same is hard with diets, but just cutting soda does seem to have a real impact.
A better analogy for the straw is skipping one fry in each meal. Technically that's an improvement, but the amount is negligible and if you act like it made a difference you're more likely to skip opportunities to actually force meaningful change.