The cartels are also extorting avocado farmers for a cut of their profits. It turns out that, if you have a lot of bad people in power, they find ways to do bad things for personal enrichment.
Why? You are punishing the avocado growers more than the cartels.
Corruption is rife. Every single transaction you make in an economy contains a percentage of evil (example: surely you disagree with some of what your government does): how did you decide that avocados are beyond your limit and carrots are not?
With the price of avocados pushing higher and higher, I think there is too much money in avocado the avocado trade. Farming is basically limited to specific areas. Lowering demand (how ever small) is making a measurable change that I fell like I am contributing to. Voting with my dollars is the only true ways to make a change. As much as this might "hurt" the farmers, it is also hurting the cartel.