I can only speak for myself, not for "the left" overall, because again, a Marxist for example would not say that "oppression is bad", they have a more materialist and anti-moralist view.
I would say that oppression is generally bad because it violates people's autonomy/personal liberty. So why is that bad? Or rather, why is personal liberty/autonomy good?
Well in my view, personal liberty is one of the few things virtually every human wants for themselves, it's one of the few things we can "agree on". Nobody likes to be a slave, nobody likes to not be in control of their lives. There are some people, for example some people who are into S&M, that do like to give up their autonomy and "be a slave", but at the end of the day, they are still the ones who make that decision on their terms.
Even the dictator or king or whatever wants autonomy, at least for themselves. The reason why they don't want autonomy and freedom for others is often because they believe that restricting other's freedom gives them even more personal freedom to do whatever they want to do.
But the thing with personal liberty/autonomy is that from a leftist perspective, it has to be "equally distributed" to people, otherwise it's not really freedom. If you give people not only the freedom to control their own lives, but the "freedom to control other people's lives", we aren't talking about freedom anymore, we are talking about oppression or even tyranny.
To use an extreme example, if there is a country where there is only 1 person with complete autonomy/personal liberty, we wouldn't call that region "free", we would probably call it a tyranny. It means that one person is calling all the shots and does whatever they think is correct without having to consider anyone's opinions.
That person could argue that they are "the most free person ever" because that person has more "freedom" than anyone in a society where freedom is distributed equally. For example, that person could have "the freedom to just have someone executed" randomly in the streets, but again, we wouldn't call that freedom, we would call that oppression or tyranny. So in order to have a free society, everyone has to be equally free, so to speak.
To come back to your question, why is oppression bad?
On a personal level, because I, like pretty much all people, want to be in control of my own life and I don't want my life to be determined by somebody else against my will.
On a more societal level, I would say that oppression is bad because it leads to tensions and conflicts between "oppressor and oppressed", which leads to instability and violence. Because of that, it's bad for everyone, even for the oppressor, because in many many cases, the oppressor will end up either receiving retaliation for his oppression or spend the rest of his life being paranoid about retaliation by the people he oppresses.
Yes, that seems to be the goal of the politicians pushing the anti-CRT narrative.
Because of the incredibly vague definition of "CRT", it often leads to teachers just staying away from any topic that could in any way be seen as "CRT". Discussing "controversial" topics can leave a teacher vulnerable for accusations by students and most teachers don't want to get in trouble, so they play it safe and stay away from the topic altogether.
Isn't that a bit naive? Of course politicians always claim that their language and thought policing is reasonable and use justifications such as "we just want to protect the children" or "it's a matter of national security"..
Depends on what you mean with "smaller government". In practice, "smaller government" often just means that big corporations get to do whatever they want. But yes, certainly in terms of language/thought policing, censorship and how much power politicians should have, I am on the side of "smaller government".