Medieval Christianity was violent and oppressive because Christianity had departed from the teachings of Christ.
Right now we have access to the Bible and, therefore, we have a sort of Christianity that is closer to what Christianity was always meant to be.
We must bear in mind that Christ is the example of conduct for all Christians.
People who erroneously believe that Christianity has evolved into pacifism also tend to believe that other religions will eventually evolve into pacifism.
This is a serious mistake that can cost thousands of lives.
For instance, Islam will never become a peaceful religion because Muhammad is the example of conduct for all Muslims and Muhammad was an incredibly violent warlord.
Therefore, any sort of reformation (i.e., return to the original teachings of this religion) will only make Islam more violent.