6 years is awfully short for this sort of thing. What we absolutely need to avoid is having justices have to care about reelection, which means we need to say justices can only ever serve one term, which means we need longer terms.
Ok "reelection" is the wrong term, but if anything this is worse, because if judges can have multiple terms then it means they're beholden to the current president when their term ends and therefore will be heavily swayed by party politics. This is why judgeships are normally lifetime roles, though the important part of "lifetime role" is "only one term" and not "never ends".
