Abstractiohn
I think that the root of the "rant" is that the writer believes that people contributing to open source "abstract" jobs from large companies. I.e. if the companies did not have access to the open source software they would pay someone to do the work in place of the open source. Hence "priveleged people are abstracting potential money from the unprivileged".
This of course also applies to people volunteering to do more or less anything in a corporate environment e.g. societies who run caffes in hostpitals, teams who tidy up railway stations and install flower beds, people who volunteer to help the down-and-outs. Software is one of the least likely candidates to abstract jobs since, in general, rather high skill levels are required.
It is based on the presumtion that 'there is work which must be done and it is either done by volunteers or paid for by "rich" corporations'. I find such a premise hard to swallow. The vast majority of Open source software is of little interest to corporations. That which IS of interest is often supported by companies providing staff to enhance or bug-fix problems in the open source software. As an example have a quick look at INTEL : https://www.intel.com/content/www/us/en/developer/topic-technology/open/project-catalog.html
Arguments will never be won against people who decide that ever person must be categorised as "an oppressor" or "the opressed". If you have spare time, you are an opressor - full stop, even is all you do is to make railway stations a little more attractive.