Does the Catholic Church today view Catholic Authority as infallible?Infallibility doesn't mean "never sinning." It "means protection from error when speaking authoritatively." The biblical authors wrote inspired Scripture, which is a far greater act, yet they were still sinners. Jesus did not promise that the leaders of the Church would never sin. Instead, He promised that the Holy Spirit would guide them into all truth --and that's a very different thing.
If it does, how can you justify evil acts by Popes?
How can you reconcile the shift of power throughout Catholic History between Counsel and the Papacy? -at times there even being more than one Pope at the same time.I am not aware of a "shift of power" in the history of the Catholic Church. Perhaps you can give me an example. I could possibly see where different time periods emphasized one more than the other, but both have always coexisted and they are not dichotomous or mutually exclusive. Popes usually consult their brother bishops before making infallible statements, and the statements of a Council are not considered infallible until they receive the approval of the pope.
And finally, how can you justify things like the Crusades and/or the Spanish Inqiusition?There is no easy answer to this question because you can answer it from so many different angles.
First of all, you have to look at these events with as much honesty and genuine scholarship as possible. Some people put the death counts up to the millions when that many people weren't even alive then. You have books like Foxe's Book of Martyrs that basically list every story of persecution available w/o worrying too much about factual accuracy. And of course, you have accounts of the crusades and the inquisitions that are agenda-driven and intended to disparage the Catholic Church. Before you can assess what happened you have to get down to the actual facts of the matter.
Secondly, you have to understand the mindset of all Christendom during these times. Truth was not treated so cavalierly then as it is now. Riots took place when heresy was proclaimed. Conversely, the entire town of Ephesus errupted with joy when the council that was held there maintained that Mary was "Mother of God." Nowadays, we can't imagine responding to truth that way, but that's how crucial it was to Christians who lived before the Enlightenment.
Thirdly, during the times of the crusades and inquisitions, there was not the severe separation of Church and State that you find today. In times where the two are interconnected, an act of heresy becomes an act against the welfare of the state. Today, we execute murderers and rapists for this reason. Back then, perpetuating heresy and revolt against Church leaders was just as serious.
Fourthly, it's unfair to paint these events as singular to the Catholic Church. In the 16th century, Protestant England severely persecuted Catholics. The Salem Witch Hunts in the U.S. obviously got way out of hand. Essentially, no Christian denomination is immune to the coersion and undue zeal for the truth that is so often presented as a singularly Catholic trait.
Fifthly, no one denies that abuses took place during the crusades and the inquisitions. As a Catholic, that's something that I just have to accept. Even in times so foreign to us now, much of the killing was unwarranted. What comforts me is the knowledge that none of the crimes committed by the Church throughout her history were truly imbued by Catholic teaching. Instead, they were motivated by sin, or by the distortion and/or abuse of Catholic principles. We have to keep in mind the fact that the weeds and wheat will exist together until the end of time and that any Catholic who acts in a way that is not in accordance with the Church cannot be said to be a true representative of Her.
Finally, there has to come a time when Christians forgive each other for the faults of the past. How long are we going to continually fling mud in each other's faces? Many popes, bishops, and laymen have apologized for the genuine abuses of the Catholic Church (for example, here). Yet, some people are simply unwilling to forgive.
I hope that answers all of your questions.