PC can become objectionable if it is a substitute for action to remedy a problem, or if it becomes an excuse for unfair discrimination. Human beings like to feel part of a group, and sometimes, in order to achieve this, put up barriers to protect the group identity and keep out outsiders. Human beings also tend to fear, or at least feel cautious towards, anything or anyone very new or different. This may be natural, but that doesn't mean it's good, or that human beings can't progress beyond these rather primitive emotions. Humanists promote happiness and fulfilment in this life because they believe it's the only one we have.
Humanists believe in using reason and compassion to solve problems.
It is in everyone's interest to oppose prejudice and discrimination, not just those on the receiving end of it. If we treated people of all beliefs and races and ages with respect, the world would be a more peaceful place. Education can reduce the ignorance and fear that cause unfair discrimination and prejudice. If you look around you with an open mind, you will see that life is much more interesting because we are not all identical.