I am in camp 4. The Internet is the biggest (virtual) metropolis around. One in a zillion is very findable when people have tools like port scanning. But you are never going to be perfect.
Therefore unles I have a good reason not to, I lock my door. I don't leave valuable lying around without reason. But I am not totally paranoid, and if you want to break the windows, I know you can get in.
But wherever I reasonably can, I pay attention to security.
Far too often people confuse being one in a crowd with being safe. That isn't true. In a world with DDoS attacks, if you aren't part of the solution, you are part of the problem...