Ma’aser Motivations

The Torah awarded kohanim with terumah gifts. After terumah was separated from freshly grown Israeli produce, the farmer would separate 10% of what remained and give that to a Levi. This is termed Ma’aser Rishon.
Talmud Bavli (Yevamos 86b) records an incident that occurred regarding a dispute between Rebbe Akiva and Rebbe Elazar ben Azariah. The exact details are somewhat murky. Further, the Talmud Yerushalmi offers details not mentioned in the Bavli. What follows is one approach to understanding the story.
Rebbe Elazar ben Azariah was of the opinion that Ma’aser Rishon was not meant exclusively for (non-kohen) Levi’im but could be given to anyone from Shevet Levi, including kohanim as well. He followed his own ruling and regularly frequented a certain garden whose owner would give him Ma’aser Rishon, although he was a kohen.
Rebbe Akiva disagreed and ruled that from a biblical perspective, only Levi’im should receive Ma’aser. Further, during the days of Ezra, Levi’im were penalized; it was decreed that from then on, Ma’aser Rishon should be given to the poor. Rebbe Akiva served as gabbai tzedakah and used Ma’aser Rishon to feed the poor that were under his care. Therefore, he was pained by the fact that, in his opinion, Rebbe Elazar ben Azariah wrongly took Ma’aser Rishon for himself. That food could have been used to feed the poor. Rebbe Elazar ben Azariah was wealthy, and Rebbe Akiva would not have given him any Ma’aser Rishon.