The staff would like cops to enact nobly their virtuous civic functions while refraining from profanity and without threatening to arrest students. While these qualities might be desirable in a proctor or administrator, were they to be adopted, they would be possibly dangerous constraints on the police.
Cursing, while vulgar by definition, is an activity not unfamiliar to even the most erudite on campus. To hold the police to a higher standard than we hold ourselves is hypocritical. At the same time, we would be forcing the police to be overly self-conscious about a non-issue. As for the question of handcuffs, the only threat police have at their disposal is that of arrest, and this threat of detention provides motivation for action.
The Harvard student body as a whole does not face police brutality. To bicker about cursing police is petty and unwarranted. In the face of real threats (like criminals and rapists), students would be only too glad for the police to muster all the law-enforcement power they possibly could, vulgarity included.