In 1934, the Tydings-McDuffie act was passed by Congress after Manuel Quezon's mission convinced them to grant independence to the Philippines. But in 1934, decolonization was not yet en vogue - France, Britain, et al had many colonies at the time, and the US had a number of other overseas possessions.
What arguments did Quezon make that were so effective at making Congress give away their land?
Quezon didn't "convince" the US to release the Philippines.
Instead, the US had always intended to grant the Philippines independence, once they were deemed fit for self-rule. The Americans viewed themselves as taking on the noble role of giving the Filipinos the education and experience necessary for independence. (Personally, I wouldn't compare the American colonization of the Philippines to the British and French Empires.)
Of course, many a rapacious conqueror in history has claimed similarly-benign intentions. But the subsequent and fairly-brief history of the Americans in the Philippines suggests that they were largely sincere and followed through with their promises:
The report of the First Philippine Commission (1899) argued that the Filipinos were unfit for self-rule and required American tutelage. (I couldn't find the full text of the original report, but this 1899 newspaper article contains some excerpts.)
The preamble of the Philippine Autonomy Act (1902) reads:
WHEREAS it was never the intention of the people of the United States in the incipiency of the war with Spain to make it a war of conquest or for territorial aggrandisement; and
WHEREAS it is, as it has always been, the purpose of the people of the United States to withdraw their sovereignty over the Philippine Islands and to recognise their independence as soon as a stable government can be established therein; and
WHEREAS for the speedy accomplishment of such purpose it is desirable to place in the hands of the people of the Philippines as large a control of their domestic affairs as can be given them without, in the meantime, impairing the exercise of the rights of sovereignty by the people of the United States, in order that, by the use and exercise of popular franchise and governmental powers, they may be the better prepared to fully assume the responsibilities and enjoy all the privileges of complete independence
This was followed by the Jones Law (1916) and the Philippine Independence Act (1934) (a.k.a. Tydings-McDuffie Act).
Of course, one could argue that Quezon was a capable leader. But just like later leaders of independence movements in the British and French colonies, the timetable for Filipino independence would probably not have been very different, even if Quezon had never existed.
Manuel Quezon had previously served as one of the Philippines' two resident (nonvoting) commissioners to the U.S. House of Representatives from 1909 to 1916. The provision for the nonvoting commissioners had been established by the Philippine Organic Act (1902) (the "Cooper Act")
While in post as commissioner, Quezon had lobbied for the passage of the Philippine Autonomy Act (or "Jones Law"), which was enacted in August 1916. This act contained the official declaration of the US Government's commitment to grant independence to the Philippines. It also created the Philippine Senate.
Quezon returned to Manilla in 1916 and was elected into the Philippine Senate. He was subsequently elected by his peers as Senate President, where he served continuously until 1935.
It was as Senate President that he led the first Independence Mission to the US Congress which succeeded in getting the Tydings-McDuffie Independence Law passed in 1934. At that point, he was able to demonstrate a record of 18 years of stable and successful government which would certainly have helped convince Congress that the Philippines were ready to become a Commonwealth - an important step on the road to eventual independence.
Quezon's best argument for Philippine independence was his highly successful record, first as U.S. Commissioner, 1909-1916, then Philippine Senator (including Senate President), 1916-34, and finally Philippine Presidency (under U.S. oversight) from 1935 onward. After he and his peers did such a good job, no one could deny that the Philippines were ready for self government.
