"A secular constitution like ours is …

  Popular mindset through unbiased education,hatred free politics ,true religious teachings can prove to be very effective in curbing this meance.Following points will help you in understanding this:
 Communalism is based on the idea that religion is the principal basis of social community. All the followers of one religion belong to one community and their basic interests are the same. It is interpreted negatively when a  group following a particular religion sees its interest as mutually hostile and antagonistic with that of another religious group.  Thus, it severs as a threat of the harmony and secular spirit of a country and is a major hindrance to democracy.

This is because

 Communalism is based on the idea that religion is the principal basis of social community. All the followers of one religion belong to one community and their basic interests are the same. It is interpreted negatively when a  group following a particular religion sees its interest as mutually hostile and antagonistic with that of another religious group.  Thus, it severs as a threat of the harmony and secular spirit of a country and is a major hindrance to democracy.

b. The common form of communalism  practised everyday is based on certain customarily beliefs,  religious prejudices, stereotypes of religions communities,  belief of supremacy of one religion over the other religions. This belief of superiority of one religion becomes the root cause of conflict in the society threatening the secular edifice of a country.