Defining hate speech isn’t practical because people will find new words. The list will grow ridiculously large until such a point as people are prohibitively cautious in even casual communication.
The criminalisation of hate speech doesn’t magically remove from a community those who harbour xenophobic instincts. It relegates them to dark corners where they find one another and exacerbate their hatred.
Hate crime is an explicit attempt to read minds. If a person has committed a crime; physically attacked another person; we already have laws prohibiting such an infringement of a person’s rights. To then go an extra step and enshrine into law the differing beliefs and opinions which could motivate an attack is without unnecessary.