You have to understand that the US military today is a very different organization than it was in the 1860s. I know - I served and majored in military history for my first undergraduate degree, and studied the civil war in particular. I also come from a military family with a father, grandfather, and uncle who served as officers until retirement age.
Far right domestic terrorism is a real and developing threat coming from both former military personnel and from civilians. The election of a far right government that shreds the constitution is also a major threat to American democracy. But if the shit does come down, it’s not going to be because some Guardsmen decide that they’d follow DeSantis over Biden.
Military justice is no joke. Falling on the wrong side of it can end people. The military is also very integrated and has political as well as ethnic diversity. I’m not saying you couldn’t find an Army colonel who wouldn’t want to engage in an armed rebellion, but the country today is very, very different than it was mid-19th century, and so is the military.
Please do note that I do see the rise of American fascism as a real threat. It’s just not going to manifest because state Guard orgs decide to disobey orders.