Most people’s values and beliefs are all wrapped up with their sense of self, so if those beliefs get attacked, they feel like they’re being attacked.
Avoiding this is very tricky and counter-intuitive, but there are techniques. Look up “street epistemology” if you’d like to know more. There’s a guy on YouTube who goes to college campuses and has discussions with passersby regarding their beliefs. Basically, it’s asking people “What do you believe?” and “Why do you believe that?” Like I said, though, it’s tricky and takes a lot of practice, and it’s really easy to fall back into old patterns again.