It's OK to get angry at stupid, stubborn people.
No, actually it is never OK to get angry at people if you work customer support. That is the business you have chosen,and I am truly sorry about that because even doing support in a small office can be frustrating. Asking technical questions, or teaching computer usage to non-technical people who do not know technology and see no reason to learn is hard.
Customer service is under appreciated and definitely under paid. As long as corporate America only sees it as a cost center or sales opportunity that isn't going to change. What we are all waiting for is natural language capable systems that can deal with people patiently and careful and so far the best we have is unhappy, under paid, under appreciated people stuck in a tiny cube farm, with limited autonomy and limited skills. This is a breeding ground for internalized rage and depression.
Whenever I am forced to talk to customer service individuals I try and personalizes the conversation, treat them as respected individuals and try an empathize with their plight. I never have a bad encounter and I hope that I have improved their day.