The biggest reason for companies wanting to protect their source code in this case is that they already know their software is broken, like pretty much every other software, and they don't want to fix it. The arguments against losing money and such are total bullshit as courts have plenty of procedures for disclosing materials only to the relevant parties present, not to the public as a whole. These companies simply don't want to spend the money auditing and making sure their code runs correctly because the only consequence of that is wrongfully convicting someone they don't give a fuck about.
I'd say, let them see the code and let the highest paid expert witness win. That is, after all, the American way.