If you accidentially add a GPL or AGPL library to your codebase your codebase doesn't automatically become GPL or AGPL. GPL and AGPL are just licenses that add restrictions that must be satisfied in order to be allowed to use the software. The worst thing a license can do is deny you the ability to use the software. If your application is not licensed under the GPL/AGPL your application is violating the copyright of the GPL/AGPL library and the author can sue you for copyright infringement which is a pretty good reason to avoid using GPL/AGPL software in a commercial setting but it has absolutely nothing to do with "tainting source code". That's just fear mongering. If what you said was the truth I'd be more worried about software licenses that force you to do absurd things like kill people. "I accidentally added a kill your wife licensed library to our company internal fork of PostGIS".