Something being open source doesn’t automatically make it safe to use. Sure, it means it’s easier for people to check for security issues, but how many people actually have the knowledge and the time to do it? And even then, take the log4j vulnerability from a while ago, it’s been present in the code since 2013 and only reported in like 2021.
Got any links to support these claims? I’d be interested to know more for when people bring up the same argument as the person you’re replying to.