As far as being assailed by highway billboards and buses covered in gaudy advertisements, these are things that I can and do often ignore. I have repeatedly driven entire stretches of highway without even noticing any billboards. Junk snail mail, although it can be annoying, is easily detected and just as easily consigned to the trash or recycle bin. Junk e-mail, on the other hand, is linear. It comes into your mailbox looking like every other piece of mail.
Some messages are recognizable by the subject line.
For example, II delete anything that has more than one X in the subject line. More annoying are the ones that try to trick me into opening them. I think there is some reason to be offended by UCE and UBE in general, but I think there's also some justification for my initial argument that not all spam is equal, despite all the people who have taken the hard line against it. We make distinctions in the everyday physical world for how people should approach us. Maybe we should make similar distinctions in the virtual world.