Sad to say, it is human nature to be uncomfortable with other races or even dislike them, particularly if they are very different from us. The contrast between humans and aliens are even greater. Therefore, the likelihood of racism against aliens is even higher.
It is hard to believe advancement of technology can change human nature. It is quite unimaginable that humans can shed their basic selfish and greedy nature and expect most of them to become kind saints.
What are some incidents of alien racism, if any, in Star Trek?