In reality, your proprietary code can only be GPLed if you explicitly release it under that license.
What people are confusing is that it is a violation of the GPL to release binary code that links (statically or dynamically[1]) with GPL-ed code without also releasing that code under a compatible license. This is where the "viral" label comes into play, since the easiest way to link against GPL code is to just make your code GPL as well. But it _does not_ mean that if you mess up and release a binary blob with GPL code in it that you've given up all rights to the non-GPL parts.
[1] LGPL allows dynamic linking, plain GPL doesn't distinguish.
I have my own proprietary code. I decide to make use of GPL code. Then I distribute the binaries. Now I have to make the source available, correct?
This source that was just made available (that includes my "proprietary code" and the GPL library I used) needs a license. At this step, I already lost my proprietary code and made it public - which might be unacceptable for some, but that in itself does not make GPL viral. Now that I need to license the released code, what options do I have? Can it be less permissive than GPL? My understanding has always been "no".
Nope! That's one way to fix the licensing issue—but you're not forced to do that.
Another option would be to immediately stop distributing your binary and not distribute it again until you can replace or otherwise excise the GPL code that caused the licensing issue.
And how does immediately stoping distribution help, legally? If I have already distributed the binary, the recipients are already entitled to the entire sources, no? Or does GPL have a "I have learned my lesson" clause?
The correct answer is that your code stealing is not transforming the product into GPL or into my proprietary license. If I catch and ask for money from you you have more options with the GPL code then with my proprietary code. With the GPL code you can just GPL your code changes, maybe the entire product but you are not forced to pay me anything. With the proprietary license though you don't have the option and I can make you pay.
So if you like that much the "infectious" word, you should add an "optional" modifier , you can always not GPL your changes, remove the "stolen" code , pay damages? (not sure if this ever happened).
What I observer the issues with GPL like software is lazy developers and companies that would like to "npm install" solutions and skip doing the work.