If you are taking a disruptive approach to the government (at any level) of a place you are traveling, you should expect to have a high risk of getting arrested, and not necessarily being given a fair trial. If you are morally so opposed to the situation that you believe this to be a sacrifice worth making, ok then. But you shouldn't be surprised when it happens.

Also, it is not too hard to imagine a foreigner's "disruptive behavior" backfiring in terms of the impact on the locals' attitude towards the policy in question. Knowing whether or not your disruptive behavior will be a useful prod to change, or provoke a backlash against foreign meddling that actually reinforces the system in question, takes a lot of nuanced knowledge of the local society, which a foreigner will usually not have.

That's a great thing you've done in Cape Town. I remember reading Trevor Noah's book where he talks about how his father challenged Apartheid with his integrated restaurant, but ultimately got shut down by government inspectors making impossible hoops for him to jump through.