True Christianity is spread by God calling people into his family and giving them the gift of his Holy Spirit who makes them more like Jesus over the rest of their life.
John 6:43 Jesus answered them, "Do not grumble among yourselves. 44 No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day.
Ephesians 1:3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, 4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love 5 he predestined us for adoption through Jesus Christ, according to the purpose of his will, 6 to the praise of his glorious grace, with which he has blessed us in the Beloved.
Ephesians 2:8 For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, 9 not a result of works, so that no one may boast.
Just because corrupt men took the name of Christ to hide their ungodly ambitions behind doesn't mean that true Christianity is to blame. If some KKK member claimed to be a Buddhist and went around lynching people who didn't convert would that mean that Buddhism should be discredited?
As to Buddhism in comparison to Christianity, Buddhism is a philosophy for this life while true Christianity is a relation with God through Jesus Christ that lasts for all eternity.
Comparison Christianity and Buddhism - What are the differences?
Jesus came to this world as a man and fulfilled all the prophecies concerning the Messiah. Buddha could not reconcile the existence of suffering with an all-powerful, loving God and so rejected the teachings of Hinduism.
There are Four Noble Truths to Buddhism: Dukkha, Samudaya, Nirodha, and Marga.
Dukkha, the first of the Four Noble Truths, says that all human experience is transient and that suffering results from excessive desire and attachment. It is a Pali word which means, "incapable of satisfying." The Buddha taught that suffering is an inescapable reality. We know there are things in this world that will momentarily end suffering. How do we know suffering exists unless we have something to compare it to? Does a man who is completely blind know when he enters a dark room?
Samudaya, the second noble truth, explains that the cause of suffering is ignorant desire.
Nirodha, the third noble truth indicates that this desire can be destroyed. The way out of suffering is craving.
Marga, the fourth noble truth, teaches that the way out of suffering is the Eightfold Path. The Eightfold Path shows the way out of the cycle of birth and death, which is full of misery. Comparison between Christianity and Buddhism can be done using the principles of the Eightfold Path:
Right Understanding - "Therefore do not be foolish, but understand what the Lord's will is" (Ephesians 5:17).
Right Intention - "He who has a wayward and crooked mind finds no good. . ." (Proverbs 17:20).
Right Speech "Everyone should be quick to listen, slow to speak and slow to become angry. . .If anyone considers himself religious and yet does not keep a tight rein on his tongue, he deceives himself and his religion is worthless" (James 1:19, 27).
Right Action - "Faith by itself, if it is not accompanied by action, is dead" (James 2:17).
Right Livelihood - "Be perfect, therefore, as your heavenly Father is perfect" (Matthew 5:48).
Right Effort - "Whatever you do, do it all for the glory of God" (1 Corinthians 10:31).
Right Mindfulness - "So we fix our eyes not on what is seen, but on what is unseen. For what is seen is temporary, but what is unseen is eternal" (2 Corinthians 4:18).
Right Concentration - "Let heaven fill your thoughts. Do not think only about things down here on earth" (Colossians 3:2). A comparison between Christianity and Buddhism reveals that both acknowledge the reality of suffering. The Bible teaches that suffering began when mankind rejected God. When we refuse to accept the reality of God in our lives, it results in suffering both for us and for those who are affected by our choices. Separation from God results in temporary suffering on this earth and everlasting suffering in Hell. Unlike Buddhism, Christianity teaches that suffering ends only in the presence of God in Heaven. We cannot get to heaven without Christ.
Buddha has shown his way to live: his Four Noble Truths and the Eightfold Path. God shows us His way; He has revealed His truth and has told us how we are to live. "Jesus answered, 'I am the way and the truth and the life. No one comes to the Father except through me'" (John 14:6).