Nice protests can be effective, especially when the people are great in number. Hong Kong protestors are trying to be civil yet still get a message across. We need to take a cue in America about those kinds of protests instead of allowing people to get out of hand as they did in Ferguson.
Yes of course I think that it is possible to protest or do anything in a nice way and get good results. Most of the time protesters are not nice and get their way but being nice good also be a good way to do it. You catch more flies with honey after all.
A "nice" protest will garner a lot more support than protesters who cause fear or disruption in the wider community. By virtue of being well behaved, the protesters will have more people on their side and, crucially, to allow people to actually hear their message. If a protest is disruptive then the message can be lost.
Though protests can begin very peacefully and with the best of intentions, it can never be nice. Many protests begin nicely and peacefully but some people may chose to become Rudy or the protest itself may rub off some people in the wrong way. Those who think that its not for their best interest may take action. For example, law enforcers can be called in to stop the protest.