[ndriscoll]

If developers became tainted by knowledge of proprietary/secret code, wouldn't you be bound for life to your first employer? And wouldn't reading GPL code like Linux also taint your mind for life? What if a coworker or some random FOSS author read the code and later used a technique they saw, and then you see it and your mind is now tainted too? Sounds like a nonsense "risk".

[fnordpiglet]

You actually are bound to not disclosure their trade secrets. Trade knowledge isn’t a trade secret, but there are aspects of their code they may consider “secret sauce,” which if you took and implemented at a competitor you better believe they will come after your employer for. I’ve seen it many times in my career over the last 30 years. Be careful, it’s absolutely not nonsense and you personally are potentially implicated.