This article discusses the fact that a young man from the UK was arrested because of racist tweets towards a soccer player. Social media has changed the way people interact and express themselves, and now it is also changing (or adjusting) the legal system.
Just like in any other circumstance, what one says is his/her responsibility. It is no different when using social media. Racist comments should not be tolerated, the same way people are held responsible for their actions when not behind a computer.