The first consequence of this is that only the copyright holder has standing to sue you, not anyone else who thinks they have a right to your code because you violated the GPL terms. They’re just wrong.
The second consequence is that the only remedies for copyright infringement are an injunction and damages related to the copyrighted code. So a court could force you to stop distributing the copyrighted code, requiring you to either (1) remove the GPL code from your product and use a substitute, or (2) pay for a commercial license from the owner. But you would not be forced to release your proprietary code under a GPL license.
Regarding jail for civil cases, no. In the US, we eliminated debtors’ prisons many years ago.
See: https://en.wikipedia.org/wiki/Sergey_Aleynikov
Most GPL projects however don't have expensive, hateful, blood seeking lawyers behind them.
Is a license violation not equivalent to unlicensed use of code?
I mean, if you don't meet the terms of a license, you're not eligible to use the code under that license. That means you have no license to the code, and therefore are in breach of copyright, no?
How is that different from just using someone else's code outright - you're breaching copyright and you're not licensed, no?
If Goldman Sachs ever officially released the software it could be a copyright or license violation but this isn't the case.