Discrimination means treating different people or things differently from one another. For example, a person who chooses strawberry ice cream over pistachio discriminates based on flavor.
Arguably, anti-discrimination laws make race, gender, and so on relations worse because they encourage people to play the race, gender, etc. card. An employer who wants to fire an incompetent black worker may hear in response, "It's just because I'm black, isn't it?" Thus the specter of a discrimination lawsuit is raised. This creates a discincentive to hire blacks in the first place. On the other hand, if affirmative action laws require the hiring of blacks, then members of races that are discriminated against in order to fill the quota of blacks (especially if those blacks are less qualified than candidates of the races that are discriminated against) may feel resentment. Walter Block wrote in The Case for Discrimination that anti-discrimination laws should be abolished, since market forces will tend to deter discrimination.
It is noteworthy that, although there are no anti-discrimination or affirmative action laws that pertain to U.S. Presidential elections — i.e., a voter is entitled by law to say, "I will vote against any black man" and to cast a vote on that basis — Barack Obama was still elected to the Presidency. This could not have happened without the assistance of voters of other races.