Perhaps it is incorrect as a legal matter. But it is not blatant disregard for the rule of law.

How does the first sentence fit with the second one?

How would using the senate to enact something which is incorrect legally not be a blatant disregard for the rule of law?

Then fifty members of the Democratic Caucus signed a letter saying they would oppose any Blagojevich appointment from being seated -- without due consideration as to whether the Senate had the right to do so. Although there is considerable disagreement on that front, it is not at all certain that they can.

The Senate clearly considered that they have the right to do so under Article I, Section 5.  How can you say there wasn't "due consideration" when the Senate is pointing to the Constitution saying, we can do this and we will.  If the SCOTUS shoots them down so be it.  But it seems to me it is their right to lose.

Either the Constitution permits the Senate to refuse this appointment or it doesn't.  There clearly are good-faith arguments for either result.  If the Constitution does, in fact, give them that power, then it's not a violation of the rule of law for them to exercise it.  And if the courts decide they don't have that power, then presumably they'll respect that decision and life will go on.  The chain of events works like this:

1. Blagojevich is the duly elected governor unless and until he is removed from office;
   
2. The duly elected governor has the power to fill Senate vacancies;
   
3. But notwithstanding that, the Senate (arguably) has the power to reject an appointee if it determines the appointment is tainted.

Suppose, to put it differently, the Senate concludes that, but for the bribery scheme, and Blagojevich's personal need to cabin the fallout from that scheme, he would never have appointed Burris.

That's not sufficient argument to deny Burris the seat.

Blagojevich's appointment is, of course, a shameful act by a disgraced Governor, a blight on the reputation of Burris for accepting, and a political embarrassment for Democrats. The proper question, however, is whether the Senate, acting in good faith, can reach a conscientious conclusion that this appointment, however unwise and unwelcome, is also unlawful under Illinois law or under the United States Constitution. If it isn't unlawful, he has to be seated.

The Senate can decide to bar Burris even if his appointment is found to be lawful, correct?  Because Blago is following the law.  

The law allows the Senate to bar Burris if they think his appointment was improper.  That's the impression I got from Akhil Reed Amar and Josh Chafetz anyway.