Engineers build small things that have huge impacts. The Linux kernel, the ARM core, the internal combustion engine, the atomic bomb.

As a profession, software engineers have very weak ethical standards. We have no Hippocratic oath, we have no iron ring. We might not be happy about it, but we'll release code that we know to be dangerously buggy, we'll cooperate with surveillance agencies, we'll design systems that exploit users, we'll build products that are sold to the governments of Saudi Arabia or Libya.

If software engineers were collectivised, we could refuse to do all of this shady stuff. Any software engineer tasked with doing something unethical could simply say "I'm not doing that, I'd lose my license". By establishing a professional body equivalent to the Bar Association or the General Medical Council, we could throw a giant wrench in the machinery of evil.

Hmm; so maybe I just misunderstood the original post at first, this or the fact that I'm already trying hard to take into account ethics in what I do as much as I can, so no big change for me? I dunno; still not quite convinced by this interpretation. I understand and endorse the idea of "picking who you work for" (though sometimes it's very nontrivial, esp. in context of big companies/corporations). I just thought that maybe the fragment about "a lot of leverage" and "small changes in what we make have huge consequences" was alluding to some other idea. Personally, I have extremely hard time seeing me choosing a different employer as "a lot of leverage" or "huge consequences [for the world]". I feel it's only a very small, though potentially at least nonzero, leverage and consequences for the world (I imagine someone else with weaker spine will hire for a particular position anyway), but in my perception notable (positive) consequences for feeling of personal integrity, though potentially (but not necessarily) at a cost for personal material situation.

Web developers of today are like the early printing press owners/operators.

I would say it depends on your position in your place of work, but there are multiple examples of this. I prefer historical ones, say for example NANP (the North American Numbering Plan).

I'm not sure what country you're in, but here, these 10 digit numbers and their various prefixes (NPAs AKA "area codes") are literally burned into the consciousness of most citizens, without them even realizing it. Additionally, all modern cellular services here are still following it in some sense or other, making it an example of highly entrenched technical debt. I'm pretty sure that the design of this system bled heavily into most other countries' telephone networks as well.

A small number of engineers probably drew up this plan on a chalkboard in the 1940s at AT&T, without a clue as to the magnitude of future ramifications.

Levarage. Enginners are generally upper middle class. Being in the middle class alone gives you vastly more freedom (ergo power) than someone who has to actively care for his needs (as oposed to surplus). More importantly, their education is above average, which is not the same as institutional education (but still somewhat correlated), meaning they'll have a better ability to analyse of what's happening, better comprehension of how change (positive and negative) happened in the past, etc. Relative leverage is relative freedom and awareness.