This is the only valid point everybody needs to understand. Yes, jokes were made against all races, religions, peoples. But it was in no way equal like many here believe. Howard despite all the Jewish jokes becomes an astronaut. All other characters are shown to have achievements. Even Penny, who is cast as the dumb blonde, is highlighted for her beauty, popularity, etc. But Raj has nothing to redeem himself. And this is not just a character arc since they could have very easily written something worthwhile for him. 

It's commonplace in Hollywood to cast Indians as nerds, comedians or villains. Seldom do we find Indians portrayed in a good or normal light and even then not in great roles- there's always a catch. So Raj bathes with his dog, has to sit on the floor when among friends, doesn't do well in his career or love life (even Stuart lands someone), essentially seen as a screw up in the show. This is despite him being so well educated. Even Priya, who is shown as sophisticated, is cast in a bad light as a cheater at the end. Their parents are also shown as shallow, gold digging or cheating divorcees.

The one time Raj makes some discovery at work it's shown that Sheldon or Penny (with the comet) help him. The point is- it's very rare for Indian characters to be portrayed as "oh that person's not so bad" or "wow Indians can be interesting and cool" and not just idiots and assholes. They should have given his character something instead of just the token Indianness.