During the G20 summit here in Toronto there were lots of protests. I spent some time wandering the internet looking for the goals of the various groups involved in the protesting and found some really interesting stuff. There were calls to violence, calls for a dismantling of the banking system, calls for the dismantling of our entire monetary system and calls for a new order of socialist rule over the entire planet. There were certainly some people protesting for useful things too as many of those heading downtown were calling for various human rights and/or environmental protection. The one really consistent thing running through these protests though was the idea that whether your hot button issue was idiotic or reasonable the best thing you could do was get to downtown Toronto to get your opinion heard.
Unfortunately that sort of rhetoric draws in those who have absolutely no idea of the issues. There are all kinds of people out on the streets protesting who have absolutely no clue about the ideas involved but are simply following along. If everyone on the streets had actually spent a full 2 hours split evenly between reading their group's ideas and a diametrically opposed group's ideas I would be much more inclined to support them - at least they know what it is they are protesting. Just getting out there lends credence to everybody already there including those intent on violence, destruction and ridiculous agendas as well as any group you might happen to agree with.
I am not convinced that huge numbers of people protesting helps much of anything at all. In particular I think that when a random person joins a massive crowd they contribute nothing towards the stated goal but rather simply put even more strain on the situation. When you as an individual know that on a given day in a given place nothing much is happening you change the situation drastically by showing up and making noise. You don't provide opportunities for violence or crime by doing so since you aren't a major event that people can use as an excuse to go wild and you don't provide a smokescreen by your numbers. You will attract some attention, though not much, but your cause will be noticed and it won't be confused with others.
When you show up to a huge event where you know many people attending are intent on violence and destruction you run the risk of being collateral damage when other people do violent or stupid things whether those people are police or protesters. It certainly feels better to be part of a crowd when making noise; it feels safer because there are others there doing the same thing. It is easier to be whipped up into an emotional frenzy and do things you would otherwise not do even if those things are simply screaming and chanting in the streets. I feel like going to an event like a giant protest of the G20 is much more enjoyable than a solo act but it is less effective at getting any particular message out and more likely to make the situation worse.