This is, of course, a matter of personal opinion. I will give an argument for each side and let you decide which argument makes more sense to you.
On the one hand, you can argue that Malcolm X hindered the cause of civil rights because he turned white people against the cause. Unlike Martin Luther King, Jr., Malcolm did not try to win white people over. In fact, up until the last year or so of his life, he was fairly anti-white. He also did not support the idea of nonviolence like King did. Instead, Malcolm was known for saying that blacks should try to gain rights and power “by any means necessary.” Because of his attitudes about whites and about violence, Malcolm was frightening to many whites. Since white people make up the majority of Americans (and were an even higher majority 50 years ago), alienating white people is a bad political strategy. We can therefore say that Malcolm hindered the cause of civil rights.
On the other hand, you can argue that Malcolm helped the cause. You can say that he did this in at least two ways. First, Malcolm helped the cause by promoting the idea of black self-confidence. Through his black nationalist ideas, he made it easier for African Americans to feel good about themselves. He made it easier for them to feel that they were just as good as whites and did not need to rely on whites. This could have promoted civil rights by making African Americans more confident and assertive. Second, Malcolm might have helped make whites more likely to accept King and his ideas. If King had been the only black leader, whites might have disliked and distrusted him. As it was, Malcolm was so much scarier than King that whites would have been more likely to support King because they might have thought that they needed to show support for the leader who was much more moderate. By showing whites what a truly radical black leader would be like, Malcolm might have helped build support for King and his policies.
Which of these arguments makes more sense to you?