SIM cards are used for transmitting voice in an insecure fashion, so you can't be sure. Some voice codecs are even designed to do something very similiar to fingerprinting voices.
> No one is taking your [...] biometric details
They were already taken when you had¹ to get the ID in the first place.
¹ The federal republic directly adopted laws from nazi germany requiring ID for every citizen. This law was initially introduced to acquire data about jews and people fit for military service.
> to match everything you ever say or do against you just to activate a sim card
This was never about surveillance by private entities! Federal agencys can match everything you say based on the fact that the SIM card in your portable bug is linked directly to you.
> but at least no one will accuse you of being an enemy of the state if you do this like trying to avoid tagging in China.
You can be certain that you end up in a database if you use a foreign SIM card from a non-KYC-country for a long period of time in a residential area. Your only defence is your network provider not cooperating unless forced by law.
Germany is being turned into a surveillance state bit by bit and I am fed up by people trying to defend it!