In this Kaliyuga there are many types of schools which are based on their believes. These believes may sometimes lead to quarrel. Without hurting their believes how we can live harmoniously?
If you understand Hindi, this video is perfect reply to your question.
Adi Shankaracharya is indeed the avataar of Lord Shiva and most of the followers of Madhva Sampradaya knows this. Just because a group of people reject the fact, you can't just blame the entire community. Focus of Adi Shankaracharya's appearance was to demolish nastikvaad and to re-establish importance of studying Vedas. Later on the Vaishnav Acharyas : Madhvacharya, Ramanujacharya, Nimbarkacharya, Vallabh Acharya and many others focused on propagating development of faith towards Supreme God Krishna or Vishnu and hence it was required to overpower the Adwaitvaad so that Vaishnavism might flourish. If Adwait siddhanta prevails, Vaishnavism will have no existence as both are contradicting to each other. This very fact both the Adwaitins and Vaishnavs should understand and thus we can live harmonically. What Wikash is saying to you is actually correct - "Respect the opinions of each other."