Yes sacrifice your livelihood so that someone else can implement the feature anyway.

Yes, that's called having a backbone, aligning your actions with your own moral code.

This is the same logic as 'well if I had quit my executioner job, someone else would have done it, therefore I am a morally blameless and non hypocritical executioner who is against the death penalty.'

Just use an ad blocker.

Obviously this is the easy solution for yourself personally. Costs you nothing, benefits yourself, allows the systemic bad practice to continue.

The actually accurate analogue would be to contribute toward actually creating or maintaining a free and widely usable adblocker, an alternate platform, to do something that helps other people overcome the problem.

I've worked a number of tech jobs and quit all of the ones that involved me directly contributing to or outright directly performing an immoral act.

I have no respect... pity, sure, but no respect for anyone that knowingly contributes to making the world worse for other people.

You are trying to form a union, that is commendable, an actual step toward positive change.

Most people?

They knowingly contribute to systems that make the vast majority of people worse off, and then bitch about other people doing the same thing in another field.

Or they don't know or care about any harm their work causes, but still bitch about everyone else doing the same thing.

First, do no harm is apparently too difficult to apply to one's own life.

If we all keep acting as cogs in the machine that makes everything worse... everything will obviously get worse.