
Many were against slavery as they had lived through forms of serfdom themselves. Others were highly educated. Surprisingly high number of socialists/communists. And it was the fact that many Germans held those beliefs that led to them being massacred by the confederates because they were seen as a threat to slaveholders and confederate power.
Most of the decline in Texas German though is mostly due to the legacy of WWI and II, as most people didn’t want to be persecuted for association with imperial Germany, or later be associated whatsoever with the Nazis, so an entire generation of children was raised without the language being passed down. In the Fredericksburg area there’s still several hundred native speakers, though most are in their 70‘s/80‘s. The youngest is in his 50s iirc.