This is almost certainly the wrong place to ask this question, unfortunately. The HN demographic is spectacularly disinterested in the well-being of humanity. Try /r/socialistprogrammers or /r/anarcho_hackers on Reddit.
Wait, what?
All anecdotal, of course.
My guess is that parent sees comments that recommend a different means to the same end we all generally believe in, and views those as disregard for humans.
Same goes for making a service cheaper at the expense of the workers and the list goes on...
You can't be binary about this.
In many situations, selling a service has made the world (or at least a city/country) a better place.
Private cell phone service in many developing countries, for example. I know countries where, before they came in, people would have to wait years to get a landline (some in excess of 10 years). Private companies swooped in and gave people access (at least those who could afford it). Imagine how limited your life would be if you didn't have any phone (and that includes no Internet).
Sometimes giving to charity is better. At other times, it's non-sustaining and you need some kind of profit model. Both can benefit society.
HN and the HN demographic are strongly interested in preserving/advancing a particular social order; one that is largely detrimental to most of humanity.
I checked that thread, and the detached subthreads appear to be either tangential or uncivil. I see little evidence of the pro-slavery agenda you allude to.
Both of these are outright lies. You can dress them however you want if you dare to reply but these are lies.
And why bother? It's not as if everyone can go check the discussion and see that these are lies. Weird.
If OP doesn't see donating to charity as interest in the well-being of society then let's just admit that the parent isn't so much concerned about whether or not HN is interested in the well-being of society so much as if HN wants to contribute to the well-being of society in the same way the parent would. Thus, parent really should say, "HN doesnt seem to agree with my particular persuasion as to how one creates well-being in society."
Donating to charity is, almost by definition, interest in the wellbeing of society.
Also, if you're going to be paid $100k at Facebook that means the value you provide is >= $100k to Facebook. It does not mean that your work is objectively worth $100k anywhere you could go. There's some correlation, of course, but I think given the context it's an important distinction to make.
As an aside, it's entirely possible for me to imagine a scenario in which the most beneficial thing one could do for society is utilize the scale and reach of Facebook. I doubt that the vast majority of the work at Facebook is that specifically, but it's certainly possible to imagine.
...or dodging taxes while getting good PR and also giving jobs to people in your own country (instead of elsewhere)?
The cost of the donation always exceeds the tax benefit.
People do things like setup foundations and then appoint people to work for them, but that still doesn't allow the money to be kept without paying taxes on it (the foundation has to engage in bona fide charitable activities to maintain tax status).
It's a failure of imagination to assume that you can do more good for the world as programmer #9001 at Facebook who donates some of his income to effective altruism than as a programmer who adds all of her value to some other cause.
Consider law, for example. To use round numbers, biglaw mid-career in NYC could target $500k/yr, and plenty of lawyers are working for non-profits at $50k/yr. So one could choose to take the $500k/yr, plus donate enough to a non-profit to hire two people full time. Now you have 2x your "more than x value".
The numbers in tech are actually not much different, for certain skill sets. It's also important to remember that skill sets are not fungible this way. I could be really good at something HFT or OR companies really want, but only middling at what a non-profit needs. This affords a sort of arbitrage opportunity.
Another option - chase a high paying career for 10-15 years, retire with a modest but secure income, move to a cheaper location and volunteer the remainder of your working life to charities.
etc. etc. be imaginative.