Eh, I had long hair for quite a while and loved it. Donated it twice, well, almost twice. Dogs thought that the drying bundle on my nightstand was a chew toy the second time around.
But try and see it from their point of view a little bit. There IS a significant bias against people with long hair. Hell, after I cut mine I stopped getting asked for a light or a spare cigarette around campus even though
I don't smoke. People are judgemental creatures and anything you do to change your appearance will also change how people see you.
Now that I've played devil's advocate I want to say that I loved my hair, I just cut it because I'm going into a competitive field where I need every edge I can get. So sure, you may love your hair. It makes you different and it makes you look how you think you should look. Just keep in mind that when going for a job interview, or an interview for college, or maybe even if you're meeting new people who can help you get ahead in life that you may want to change your appearance. The great thing about hair is that it grows back, so once you've made a good impression (they really do matter, look up the anchoring and adjusting heuristic) and won the person over with your personality you can grow it back out again.
It's easy to get indignant when people tell you to change something about yourself and it's hard to actually listen and consider where they're coming from, but they might actually be trying to help. It'd be like seeing someone limping around too proud to use a cane, but on a lesser scale of course. Now if you're NOT going into a well established field controlled by a dominant image (medicine, law, etc.) then it really doesn't matter as much. Technology is a newer field and more progressive, so a pony tail won't exactly set you back as much from what I've seen.