First, the Catholic Church was NOT the first Christian church. Mary you'll learn this in college. Or get a head start and read some of Elaine Pagels work. Adam, Eve, and the Serpent, The Gnostic Gospels, Beyond Belief. Or try Carl Sagan's The Demon Haunted World.
Second, the protestant churches also persecuted and murdered and tortured those who would not convert. Anyone remember Cromwellian England? If you were Catholic and not murdered (burnt alive) then Cromwell's men sliced off you nose and ears. Michael Jackson would appreciate this --- so many aristocrats (mostly women because their husbands were murdered) lost their noses that a fashion of fake noses began! Yeah really!
Or even better how about the British Empire under Queen Victoria and the sub- continent of India remember the black whole where the "heathen" were slaughtered because they were well, heathen?
Third, Or (not to pick on the Brits alone) how about those Pilgrims (Puritans --- hmmm wonder why they called themselves pure? Because they new they had the one pure faith?) who came to America for religious freedom and proceeded to murder anyone who questioned the "brothers". Those witch trials were a copy cat serial killing from the dark ages. Also, let's take this up a knotch to the 1960's in the southern states where more than one Catholic priest was lynched by YES I'm gonna say it even though I live in the south --- Baptists (weren't they originally Dutch?).
And again if you think that Catholics were the only converter/murderers; consider the Islamic potentates who occupied Spain and converted not only people (killed the men, raped the women) but churches too (Muslims did this to the Eastern churches too ex., the Hagia Sophia and the Alahambra in Spain.)
The French revolutionaries (Marat Sade, Robespierre, Danton and you know the rest) ordered the killings of the Catholic priests during their revolution.
In Asia, including the islands of the Pacific many Protestant missionaries were killed by local shaman of tribal religions. This also happened in Tibet by the Lamaist Buddhists (Yeah, these guys aren't all peace and love).
Come to think of it, the Israelites killed, maimed, raped, burned, conquered any nation who would fight them and some who wouldn't.