It’s not “assumed to be secure.” The source code being publicly available means you (or anyone else) can audit that code for vulnerabilities. The publicly available issue tracking and change tracking means you can look through bug reports and see if anyone else has found vulnerabilities and you can, through the change history and the bug report history, see how the devs responded to issues in the past, how they fixed it, and whether or not they take security seriously.
Open source software is not assumed to be more secure, but it’s security (or lack thereof) is much easier to verify, you don’t have to take the word of the dev as to whether or not it is secure, and (especially for the more popular projects like the ones you listed) you have thousands of people with different backgrounds and varying specialties within programming, with no affiliation with and no reason to trust the project doing independent audits of the code.
Assuming 12oz beers at 5% ABV, that you’re a man at the global average weight of 180lbs, and have a healthy liver, if you paced yourself to 1 beer every 1.5 hours over the course of your 16 waking hours per day, your BAC would never exceed 0.02, you’d have 5-10 minutes between beers with a BAC of 0, and you’d drink about 12 beers in a day.
Most people would not be noticeably intoxicated by this and probably wouldn’t experience any kind of hangover. They might wind up a bit dehydrated if that’s the only thing they drink. It’s also definitely not advisable to do that over any extended period of time.