Loyalty:

[In the Hamdan decision,] Justice Thomas refers to Justice Stevens' "unfamiliarity with the realities of warfare"; but Stevens served in the U.S. Navy from 1942 to 1945, during World War II. Thomas's official bio, by contrast, contains no experience of military service.

Looks like Harry Reid was right when he was on Meet the Press talking about a possible new Chief justice:

RUSSERT: Why couldn’t you accept Clarence Thomas?

REID: I think that he has been an embarrassment to the Supreme Court. I think that his opinions are poorly written. I don’t–I just don’t think that he’s done a good job as a Supreme Court justice.