Mahatma Gandhiji execution

Mahatma Gandhi was not killed because he was the only one who stood between Britain and a complete anarchy in South Asia. Besides, Mahatma gave no quarter or justification for the British to execute him on a capital charge. The British Raj in India gave a pretense of fairness and found it hard to charge anything big. Executing Gandhi would have broken the ruse they were ruling India with - "Western nation civilizing the barbarians". Gandhi knew exactly what he was doing.

By early 1920s, India had gotten extremely restless. In a small city in northern India, British Raj was shown how helpless it could become when surrounded by angry villagers. Chauri Chaura incident 1000s of angry Indian men locked up the British police constables and burned the police station. With less than a million strong military force and 500 million angry Indians, it was a highly mismatched battle. British Raj could have ended in no time.

Mahatma, the man of honor, took responsibility for the disturbance and called for a halt to the protests. He insisted on India achieved her independence in an orderly fashion. That bought time for both India and Britain.

Without Gandhi, the trajectory of Indian independence movement could have been very different. India might have probably got the freedom sooner, but at an extraordinary cost to both Britain as well as India (although it is less likely that India would have been one nation). In short, it would have been idiotic and short-sighted for the British to shoot the Mahatma.

Let us also think of the different time windows in which he could have been executed:

World War I: This was the time when Mahatma entered Indian politics. He was a much lesser threat. Also, he helped Britain secure Indian popular support for the war. Mahatma hoped that Indian kindness would help Britain act more humane. Things worked in the reverse after the war.

1920s: By now, Mahatma had a large following in Britain. Shooting him would have been disastrous for the political party in power. 1920s was a time where both Labor and Conservatives were winning with razor thin majorities in Parliament and often hung Parliaments. UK had 4 elections between 1918 & 1923 and both parties were quite unpopular at that time.
1930s: Mahatma had been already in the jail for a good chunk of the period. Britain showed more openness in talking about the India issue.

1940s: Mahatma was again in jail for most of this period for his involvement in Quit India movement. US was also very sympathetic to Gandhi's cause and FDR was strongly pressing in Britain to show more leniency. Churchill, for all his hatred for Gandhi, could not afford to alienate a big ally.