The misconception is that he personally cared about the direction of outcome, not that the council he created actually did these things. Like it says, "In fact, Constantine had little theological understanding of the issues at stake, and did not particularly care which view of Christ's nature prevailed so long as it resulted in a unified church." He didn't sit down and say, I want Christianity to meet these criteria because I'm a Christian and I have faith in Jesus as god, he said make the Christians unified at any cost and write whatever you decide about this shit in stone so I don't have to deal with them arguing anymore. Christians did not agree with each other, and he forced them to without any real regard for the religion himself. Prior to his actions, many Christians did not believe Jesus was god incarnate, amongst MANY differences in the then 300 year old stories. There were many religious texts that were left out of the bible, if this was not true there would have been no need for the Council of Nicaea as none would have had differences in opinions about the very fundamental principles of Christianity.
This is also evidence as to Constantine's atheism, to historians he is "widely regarded" as an atheist because you can see his "faith" is pretty clearly a political tool due to his psychopathic adaptability to change the core of his own belief structures for simple political reasons. The only people I know of that think Constantine was really a Christian are generally people that just learned about him, and want him to be Christian. If he really was a Christian to the point where his faith moved him to publicize Christianity, don't you think he would have had an opinion on whether or not Jesus was in fact god or not, or simply a good man/prophet?
Any way you look at it, Jesus Christ wasn't accepted as "god incarnate" by those who believed in Jesus until Constantine forced the issue to be settled due to the fierce debate getting to the point of dividing his political constituents. It was about 300 years after anyone alive during the time of Christ was long gone, there were books that portrayed the childhood and many other "eye witness" events of Jesus left out due to them humanizing him too much. Jesus wasn't declared as god incarnate because of widespread belief by Christians that it was true, it was because hand picked politicians made the choice and crafted the materials that would spread their beliefs. The goal was clearly unification, not historically justified accuracy.
There was information that did not align with the version of Christ they were pushing to solve their political problems, so it was left out and declared to be written by false authors. Constantine himself may not have determined which solution was chosen, but it was only due to his influence that either one was accepted. The fact that he did not care enough to decide how the religion turned out other than "stop arguing and be in my military" shows that his commitment to his faith was essentially nonexistent, yet the power he held over it was very real.
Edit: I've been reading more about Constantine.
It's kind of absurd how much disinformation there is about Constantine the Great. Nobody really agrees on all the details. I'm trying to draw conclusions based on the things people do not argue about.
Some people say he didn't have much of a say in the divinity of Jesus discussion, others say that his mere presence formed the opinions of the Council, and others say he declared Jesus was god himself. Nobody however disagrees that the reason he forced a decision was in order to unify his people in order to prepare for war, and to maintain control of his kingdom.
Many people disagree about his relationship with Christianity. Some say he was an atheist, some say he was a pagan, some say he became a Christian and then legitimized Christianity, others say he used it only as a political tool and remained an athiest/pagan his whole life, and even others say that he did not convert to Christianity until his deathbed. The things people don't disagree about, is that there is at least strong support that he may not have believed in Christianity (he was a high priest of a pagan religion prior to promoting Christianity), he definitely used the religion as a political tool, he at least considered unifying people under pagan gods but in their mythology they didn't protect those who believed in them, and that he was not baptized until just prior to his death (long after the council of nicaea). There are many people that have used religion to further their own goals, but the question comes up specifically about Constantine's faith so often because he did not act like a Christian in any way, and politically Christianity was adapted to serve his needs, rather than vice versa.
I personally believe that he was a political opportunist, and that simply the vast amount of disagreement and misinformation on the beliefs, methods, and goals of Constantine yields substance to the existence that the bible itself was made as a tool of political disinformation, much like the documents that talk about its creation at the time. Christianity as it exists today was not formed transparently by those of strong faith, its beliefs were selected by politicians trying to unify a nation for war any way you look at things.
Another broader overview:
http://www.essortment.com/constantine-g ... 21913.html
Examples of things left out (talks about Jesus's childood, makes him seem kind of evil):
http://www.earlychristianwritings.com/i ... homas.html
Modern Faithful Christian's opinions:
http://www.christianforums.com/t7549453/
More about alternative christians beliefs:
http://www.bartdehrman.com/books/lost_scriptures.htm
To be honest, was actually one of the reasons I started not believing in God.