Human beings have their own ways to express their feelings of grief and sadness as well to express their feelings of happiness. Islam allows different ways of expression of feelings as far as it does not contradict a clear ruling of Islam. No one can express his happiness by dancing, simply because dancing is forbidden in Islam. No one can express his sadness by drinking beer or alcohol, simply because drinking alcohol or beer is forbidden in Islam.
People whom you mentioned in your question are expressing their feelings of grief by their own way which does not contradict with any Islamic clear rule, and does not have bad effect on the image of Islam.
Allah (SWT) grants people the reward according to their intentions. These people are observing and remembering the tragedy of Karbala. May Allah (SWT) grant them reward according to their intentions.