The use of "to give" is not necessary in this sentence, because "ought to do" is used. Ought is an auxiliary verb (a verb that expresses an aspect of another verb, such as: be, have, will, shall, can, may and do). In the sentence above, "is give" is the predicate. "To give" can be used in the sentence if you change the sentence structure and omit "to do". Example: "We ought to give to people we love." I hope my explanation was helpful.