It’s ok to be mad at a company if they fuck you over by rescinding a signed offer.
Yet a lot of people get angry easily, and being an easily-triggered person works against a person's life. No one wants to constantly have to walk on eggshells around another person in order to be their friend, partner, child, etc.
Personally, I don't enjoy the emotion of being angry. If you do, more power to you.
no one cares
Getting angry is optional. With some practice (largely, mindfulness) people can learn to notice their emotions and not become strongly identified with whatever is happening in the moment, and choose to do something more productive than simply stewing or ruminating in the unfairness of life.
Thanks for engaging.