Good question. If you have a reasonable expectation that your participation in an event will result in your party instigating violence (like you bring or stash weapons, create plans for high-ground, etc.), then you're probably in danger of an ethics violation. If you're advocating for the ethical use of information and promotion of privacy in a peaceful manner, you're probably fine.
Hi Jess. What a great question to begin with! I think we have to start with the Canons of the (ISC)2 Code of Ethics to answer your question:
There is nothing in the Code of Ethics that restricts you from voicing your opinion in a legal way. In our society you have the right to free speech and nothing can overrule that, not even being a member of the most awesome group of security professionals. You believe that net neutrality is important for society and you want to defend that. That's 100% in line with Canon I of the Code of Ethics so I don't see any problem there.
Canon II tells us to "Act legally". For the sake of simplicity I am assuming that you are not planning to perform any legal acts while partaking in the protests, so I think there is no issue here either.
The last 2 canons are more related to your work for organizations, clients and employers as well as serving the profession in general. It is extremely important to note that the canons are put in a very specific order. As an example, your employer could ask you to install a snooping device that would intercept all internet communications for all citizens in the United States. While it would definitely be in line with Canon III, a complaint could be raised based on Canon I (protect society) or Canon II (act legally) without much push back at all. This is what it means to hold ourselves to a higher standard.
I hope this clarifies your question.
Disclaimer : I am the current chair of (ISC)2 and the Ethics Committee works under my leadership. This post is not formal guidance from (ISC)2 or its Board and purely reflects my personal opinion based on the information you provided in your question.
I hope you read Wim’s post. He has posted sage advice.
Personally, I think we should stand up for net neutrality!
If you do go, please do make sure you are safe and have alternate ways to leave. As you have said, odd things have happened - even at a peaceful protest.