Basically, kangaroo court is a term somebody used once to describe what he felt was a sham of justice and and it caught on. It's used today by people who don't wish to recognise the authority of a court. That could be for many reasons, subjective reasons, where one person might say "yes I agree that's a sham of justice" and another might say "I think it's perfectly just" and we have a fucking debate about whether a court is a kangaroo court and it's a debate nobody wins because there's actually no such thing as a kangaroo court other than in baseball.