(This post was published as an op-ed in The MetroWest Daily News, click here.)

There are many qualities that excellent justices require. First is what is called the judicial temperament; that is, according to the American Bar Association, “compassion, decisiveness, open-mindedness, sensitivity, courtesy, patience, freedom from bias and commitment to equal justice.” Second must be a thorough knowledge of the law. But neither of these are of much use unless the judge shows consistency; consistency in outcomes for similar cases, consistency in the logic used to reach those outcomes, and consistency in what is and what is not allowed to influence the decisions.

If these characteristics are desirable in a trial judge, how much more necessary they are in a Justice of the Supreme Court of the United States. Yet Chief Justice Roberts has shown himself to be lacking in consistency in the reasoning behind his decisions. We need to make a close comparison between the recently decided McCutcheon case (McCutcheon et al. versus Federal Election Commission, 2014) and an Arizona Case decided in 2011 (Arizona Free Enterprise Club’s PAC et al. versus Bennett, Secretary of State of Arizona, et al., 2011).

In McCutcheon, Roberts makes very clear that speculation of what might occur (such as the funneling of excessive funding to a candidate or party through a complex of committees) is irrelevant in deciding the issue. Only verifiable events that have actually occurred can be considered as evidence in this case. He writes:

“And” importantly” we “have never accepted mere conjecture as adequate to carry a First Amendment burden.” Nixon v. Shrink Missouri Government PAC, 528 U. S. 377, 392 (2000).”

He is saying here that one must have a strong, factually based argument in order to make a decision involving the freedom of speech. In fact, such joint committees already exist and Washington lobbyists like Covington & Burling are celebrating:

“we expect today’s decision will increase the political power of Members of Congress who have a strong relationship with high net worth donors. We also expect it to increase the influence of major donors.”

However, in Arizona Free Enterprise, he took a quite different tack. The Arizona law provided public financing to candidates whose opponents exceeded a threshold amount of private funding. At first glance, this would appear to fulfill the requirement that more speech (or money in Robert’s view) in an election is better. However, Chief Justice Roberts speculated that the existence of the threshold would create a disincentive for privately financed candidates to raise and spend as much as they could because this would trigger an additional public financing for opponents. Thus the law inhibits, according to Roberts, the free speech of the privately financed candidates. Here speculation, based on very little evidence other than affidavits from political candidates stating that they believed that if public funding were available, they would have been unable to raise money, is admitted as a fundamental rationale for the striking down of the Arizona law.

It would nice if Chief Justice Roberts was consistent in his rejection of speculation in these cases. Just as it would have been nice if he had upheld the doctrine of “stare decisis,” which he promised to do at his confirmation hearings.

Justice Roberts is unreliable. The American people deserve better of the Chief Justice of the United States.

Martin Evans is on the governing board of Common Cause Massachusetts.