Question

why the opposition parties of India cannot fight unitedly in any problem?

Answer 1

It’s believed that Indian polity has been able to sustain its democratic nature because of the constant scrutinizing by  opposition parties. 
A party might not be able to form the government at the center because of the lack of majority, but that doesn’t take away the responsibility of acting as a watchdog of the ruling party. 
When it comes to questioning the government and preventing them from taking negative strides, parliament is the most suitable platform for the opposition to leverage.

Answer 2

Explanation:

This hate is new only, if you see in history where Rajeev Gandhi sent Atal bihari Vajpayee to United Nations to represent India.

And Atal Bihari Vajpayee so many times mentioned Good work done by Indira Gandhi , Jawahar Lal Neheru in parliament.

They always called a all party meetings to resolve internal issues.

everyone used respect others.

Now politics is in worse stage, its not personal hate against rival party members.