Kennedy is not considered a liberal justice because during his tenure on the Supreme Court, he often sided with conservative justices on key issues. He was known for being a swing vote, occasionally leaning towards more liberal positions on certain social issues, but overall his voting record aligned more closely with conservative ideologies. This is in contrast to justices like Sotomayor, Kagan, and Breyer, who are generally considered to be more liberal in their judicial philosophy and voting patterns.