It's more about preventing companies like Facebook getting their hands on everyone's data and abusing it as well as preventing organizations like Signal themselves using / abusing this data. We won't ever truly know if Signals data makes it's way into the hands of government security agencies but I would say it more than likely does or it will if they want it to in the future.

If some government wants to get you they will get you, probably via your operating system... Signal won't help you. If that's your concern then you gotta stay off the internet to be honest!