Regardless of all these other things, there are also situations in which the collective-action any individual might choose (even for selfish reasons!!) if they had the magic button is not the action they would choose as an individual without the coordination of others.
So, however it is accomplished, in whatever political system, there are cases where merely enabling a group of people to act in coordination allows them all to pursue their individual interests more effectively.
The core point being: you cannot merely judge that people who refuse to unilaterally follow a contract that others reject means that those people do not support the contract.
Put another way: Kant's categorical imperative is a nice concept, but it's delusional to actually think it represents reality rather than just a mental model.
If I self-sacrifice without collective action, I might very well reduce my own capacity for other positive actions and convince others by my example that self-sacrifice is counterproductive.
Liberal ideology requires a god-blessed sovereign that lives outside of the system and has no motivation other than the common good for his subjects - whether that's a king, a magical computer that makes provably optimal inhuman (i.e. objective) decisions, or an army of biracial, bisexual, ungendered university professors who were in the top 2% of their class in elite colleges. There is no government, and no means of governance, that lives outside of the human struggle for power. Governance is the wielding of power.
You can't just wait for power to be placed in the hands of the just. The just are the ones who are willing to forgo power for the sake of the good. There will never be a magic button that you can push to make everybody stop benefiting from the bad thing at the same time. The kind of government intervention you're asking for is divine.
You have to take a risk, to be weak on purpose. Hobbes said it best in Leviathan: you have to make a "covenant" with the world, a contract that you will follow for the sake of others whether or not others follow it. An oath that obligates you and no one else, with the hope that others will be inspired by your vision for the world and live the oath themselves. The combination of you and those others creates power.
[$] Everybody is willing to be inconvenienced in some way for some value, everyone has some value that when violated will effect their personal comfort more negatively than some marginal degree of convenience will improve it.