This quote seems like it's lumping every process for arriving at beliefs besides reason into one. "If you don't follow the process I understand and is guaranteed not to produce beliefs like that, then I can't guarantee you won't produce beliefs like that!" But there are many such processes besides reason, that could be going on in their "hearts" to produce their beliefs. Because they are all opaque and non-negotiable and not this particular one you trust not to make people murder Sharon Tate, does not mean that they all have the same probability of producing plane-flying-into-building beliefs.

Consider the following made-up quote: "when you say you believe something is acceptable for some reason other than the Bible said so, you have completely justified Stalin's planned famines. You have justified Pol Pot. If it's acceptable for for you, why isn't it acceptable for them? Why are you different? If you say 'I believe that gays should not be stoned to death and the Bible doesn't support me but I believe it in my heart', then it's perfectly okay to believe in your heart that dissidents should be sent to be worked to death in Siberia. It's perfectly okay to believe because your secular morality says so that all the intellectuals in your country need to be killed."

I would respond to it: "Stop lumping all moralities into two classes, your morality, and all others. One of these lumps has lots of variation in it, and sub-lumps which need to be distinguished, because most of them do not actually condone gulags"

And likewise I respond to Penn Jilette's quote: "Stop lumping all epistemologies into two classes, yours, and the one where people draw beliefs from their 'hearts'. One of these lumps has lots of variation in it, and sub-lumps which need to be distinguished, because most of them do not actually result in beliefs that drive them to fly planes into buildings."

The wishful-thinking new-age "all powerful force of love" faith epistemology is actually pretty safe in terms of not driving people to violence who wouldn't already be inclined to it. That belief wouldn't make them feel good. Though of course, faith plus ancient texts which condone violence can be more dangerous, though as we know empirically, for some reason, people driven to violence by their religions are rare these days, even coming from religions like that.