Hero or Villain?

I remember sitting in a NieuCommunities curriculum session two years ago listening to a veteran church planter speak about the history of the Church and he spoke about Constantine and in a way villified him for legalizing Christianity in the Roman Empire. I bring this up because I am currently reading Church History in Plain Language (2nd ed.). It has an interesting take on this currently controversial Roman emperor. For those of you who are possibly unfamiliar with his story, Constantine was a Roman general proclaimed emperor by his troops at what is now York. He faced a strong opponent in Italy and crossed to the continent to face him. Before his epic battle at Milvian Bridge against his rival, he saw saw the a Christian symbol in the sky (I would guess it to be a chi-rho) and heard a voice saying "by this sign you will conquer." Constantine proceeded to order his troops to paint their shields with it, and he indeed won the battle. From there Constantine made Christianity a legally recognized religion in the empire, ending centuries of persecution. This came with several benefits - the church now was able to breathe and enjoyed the freedom. It was a period in which some of the great doctrines of our faith were decided, but it was also a time when the state now controlled Christianity. This led to the rise of the papacy as the head of all peoples in medieval Western Europe.
The author of the book makes a case that perhaps this was needed as less than 200 years later the western empire collapsed under waves of barbarian hordes. It got me to thinking. Maybe God allowed this event to happen so that His people in the west would be protected when their way of life collapsed. I'm not going to say that there wasn't a lot of abuse. However, the eventual rise of the popes meant that Christianity was not only saved in the west but was preserved in the face of overwhelming odds. I don't know what I think about it. However, I am now more hesitant to critisize it. We never know what or who God will use for the furtherance of His kingdom. What's your opinion?