I think Voltaire said it pretty succinctly.
"Those that can get you to believe absurdities, can make you commit atrocities."
"Those that can get you to believe absurdities, can make you commit atrocities."
You'd believe if you just opened your heart" is a terrible argument for religion. It's basically saying, "If you bias yourself enough, you can convince yourself that this is true." If religion were true, people wouldn't need faith to believe it -- it would be supported by good evidence.