This is better than not having the code at all, however this is a false sense of security.
First of all, you should be compiling your own binary from the sources, otherwise you are blindly trusting that those binaries you download are built from the original source code, which may not be the case.
Second, open source security relies on enough eyeballs reading the code independently and spotting the security holes or anything malicious but you can't know how many people actually did. Some software isn't popular enough, some other software contains millions of lines of code.
The same process would have to happen for each patch and software update.
The same thing happens with closed source projects, however. Less popular software will have smaller staff and it's more likely to contain errors and security holes, especially if it's an one man project. More popular software will have more staff working on it but if the software is big and complex, most people working on the project have never read the entire code and there's more lines of code that may contain issues.
Software is a giant mess
Of course, you can make money using open source software to provide solutions for your clients. If you run a SaaS you most likely built it on open source software, and ironically, exert even more control over your customers.
But what if you simply want to sell your open source product to customers so they can run it themselves? It's a dream for many developers but impossible to achieve. There are some success stories, but they are always the exception not the norm. And they often require selling closed-source extensions that are the bits of the business that actually bring in revenue (think GitLab).
And no, you can't sustain your livelihood by selling support if you are a solo developer. Besides the idea of selling support for open source products is, to most developers, the most unappealing option possible. (Charging for documentation is even worse.)
The GNU Project (supported by the Free Software Foundation) still "encourage people who redistribute free software to charge as much as they wish or can" [1]. This advice might have made sense in a time of software CDs and dial-up internet, but makes no sense in a era of broadband and GitHub.
As a matter of fact, one of the guys in that Twitter thread, Olivier Tassinari - a team member for the Material UI react component kit, acted like he was some kind of royalty when he compared his GitHub contribution history with mine after a disagreement about putting ads in NPM logs.
I can't stand arrogant, entitled assholes like that, especially when I'm supporting everybody by regularly donating money to much, much larger open source projects that everybody uses.
"Well, if not contributions, at least it will help with your career, with consulting work or job offers."
[1] Yes, even slapping the BSD license and doing nothing is effort. And odds are good you'll not get anything out of it.
(Some will. Most who are express it correctly by never contacting you.)
The reality is popularity and budget are more relevant than licensing in that regard.
Say you pay 1M EUR to Microsoft for their suite, 10k users.
You get an asset manager and a IAM (AD), database, web server, OS, user desktop, word, excel,...
All of this integrated.
On the other hand you have all the pieces separately, maintained or not, and they do not talk to each other.
You saved 1M EUR, which will give you a team of 5 or 7 people who are supposed to maintain and integrate these pieces (the part of work MS does, not the administration you need anyway on top).
It may work or not, but this is far from a given.
If I had to start the IT of a company today I would go for full SaaS for services, Win10 on desktop, and O365.
(just in case and to avoid misconceptions: I like my Win10 desktop much more than a Linux one (tried to switch multiple times in 20 years), run all my home services on Linux and develop open source)
Someone is paying the price for open source software. Employers, employers being stolen from, individuals using their spare time, individuals who have been given/made a lot of money or the state.
I worry for younger people who have an over romanticised view of open source and would ask that they consider how their open source heroes created their software. Were they supported by academia, employment or the state? Make sure you can pay the bills before you think you are ARPANET or Linus Torvalds. Make sure the 100/0s of hours invested were a good use of your time.
The more the better. - The contrary is true. The busfactor is only relevant to closed source. Design by committee works nowhere. Not in the arts, not in engineering.
The project is not maintained anymore, the latest issue or commit was years ago. - This defines stability. no problems, no changes needed.
That is the biggest lie I see. It falsely equivocates a project’s security to its popularity. This is the primary adoption consideration for most JavaScript projects.