How can anyone be a Catholic is beyond reason…..

[Baruch]

It wasn't because of disagreements about epistemology (what is true and how can we tell).  It was because the Church by and large until 1500 was the continuation of the Roman Empire in a new form.  And Rome is always expanding, always conquering, always enslaving ... just like it always was.  This wasn't a bug, it was a feature.  Ask anyone subject to Roman tourists:

"PLUNDERERS OF THE WORLD, HAVING EXHAUSTED THEIR LANDS WITH INSATIABLE LOOTING, THEY RANGE ACROSS THE SEAS. THE WEALTH OF ANOTHER COUNTRY EXCITES THEIR GREED; AND IF IT IS WEAK, THEIR LUST FOR POWER. NOTHING FROM THE RISING TO THE SETTING OF THE SUN IS ENOUGH TO SATISFY THEM. AMONG ALL OTHERS ONLY THEY ARE COMPELLED TO TAKE FROM THE POOR AS WELL AS THE RICH. TO ROBBERY, OUTRAGE, AND SLAUGHTER THEY GIVE THE LYING NAME OF FREEDOM; AND WHERE THEY MAKE A DESERT, THEY CALL IT PEACE." TACITUS

And the post 1500 world, including the US, are largely a re-vived Roman paganism.  This is why the US loves perpetual war in the Middle East.  Tacitus might have as well quoted Dick Cheney.