Majoritarianism is a process in which a country gives priority to the religion in majority.

It harms a country as the religion in minority gets depressed and suffers a lot.

This can be explained with the example of Sri Lanka as majoritarianism is followed their giving priority to the Sinhalas.

Majoritarianism in Sri Lanka.
 

The leaders of the Sinhala community of Sri Lanka sought to secure dominance over government by virtue of their majority.

(ii) In 1956 an Act was passed to recognise Sinhala as the only official language, thus disregarding Tamils.
(iii) The government followed preferential policies that favour Sinhala applicants for university positions and government jobs.
(iv) In Sri Lanka, maximum people believe in Buddhism. A new constitution stipulated that the state shall protect and foster Buddhism.

This led to civil war