Harvard University’s $34 billion endowment has received much scrutiny in the last year, with critics questioning why the university doesn’t spend more and some lawmakers looking for ways to tax it. Drew Faust, the university’s president, used a commencement speech Thursday to defend the institution’s endowment as necessary and to question those critics. Some see endowments as “vast pots of money for presidents to spend at will,” she said. Others say endowments must be devoted to “educating the most students at the lowest cost.” Faust noted that much of the endowment is restricted — she cited examples of funds to buy meteorite specimens or plants that reproduce via spores. If Harvard spent more of its endowment funds, it would have less annual support for its budget, Faust said, and that would mean “less research, less teaching, at a lesser level of quality.” Further, she said that endowments must be viewed in the context of the needs of future generations, since donors gave to support Harvard over time. “It means we cannot treat our endowment as a lump sum to be spent on the projects of any given cohort of faculty or students, the demands of today’s politics, or even the vision of an individual Harvard president,” she said.