There are a number of reasons that some people don't like MMA:
People look at it as being shear brutality, with little in the way of sport to it, it is simply guys beating on each other attempting to hurt or knock them out.
It is treated as a sport instead of a deadly skill.
Because the Mixed Martial Arts competitions ignore the traditions of the martial arts.
Many traditional martial artist look at the rules and artificial limitations placed on those that concentrate on the competition rather than the skills and techniques involved. For this reason, many traditional martial artist will not compete because it restricts choices and limits reactions. (If someone attacks me, I will gouge their eye out or dislocate their knee with a kick.)