The officer is perfectly within his rights to ask questions and to observe the individual. The individual is perfectly within his rights to refuse to answer the questions. I'm pretty sure that any officer outside of Barney Fife would be able to figure out if the individual had something on his person that he might be planning to throw over the side, and in that case the officer has reasonable suspicion to detain the potential brick-thrower.
And what difference should it make whether it's my mother, your mother, or nobody's mother?
That's wishful thinking on your part. People who want to give up a degree of safety in order to retain personal freedoms usually have a very good idea of the risks involved. People who demand more protection from the government, and are willing to give up those freedoms in order to get it, rarely go through that thought process.
Those who complain about police overstepping their bounds will always be the first, and the loudest, to whine when police don't stop crime...