Find a thread where someone is looking for a piece of FOSS software and someone comes in saying "I've tried all the FOSS projects, but I find X [paid or not open source] just works better for me" and you will see the reaction you want to see.

Like vegans, FOSS people are a minority community with stiff moral stances and they hold their beliefs for very specific personal reasons. To the FOSS people, suggesting they use closed software is likely the same as when people tell you that you must not be getting enough Vitamin B or whatever because you don't eat meat.

As someone non-vegan and not overly concerned about FOSS, I've had guys and bad interactions with both groups. I've had bad reactions when I've suggested free but closed source solutions and gotten bad reactions in return, and I've shared things with vegans who liked my original things I've shared about meat and dairy alternatives and their opinion of me changes when they learn I hunt for food.

People get defensive when you either question their morality or people question your morality. We can attempt to understand others' actions and beliefs, but we truly only understand our own, and that can make us all act out irrationally. It can be hard to not try to show others why you made your personal moral decisions, and it's fine to try to share or teach others your values, but there's a fine line between sharing beliefs and getting pushy about it, and it's different for everyone.