Should bicyclists know traffic rules?

When reading on a news item where a car hit two children at a zebra crossing, I encountered several people who were saying:

"Because bicyclists do not have to go to driving school and they do not need a license, you cannot expect them to know traffic law".

This is nuts. It's a general principle that all people are supposed to know all laws that apply to them, even though they have not passed a law degree in university. Not knowing a law is no grounds for not obeying it. That is a good reason to keep legislation simple, so that all people could understand it and obeying the laws is reasonably possible.

Yes, there are lots of car drivers who don't know the rules either. Some of the Finnish traffic law is actually rather unclear and poorly formulated - like the roundabouts, which are not really covered in the law resolutions of the government; here Finland is closer to Anglo-Saxon case law, which I think is a bad thing. Or the rules regarding crossings of regular roads and bike roads, which were changed a few years back and although clear in law text, are unintuitive, and most people don't know them correctly. But many bicyclists also seem to have serious attitude problems towards traffic law.

One thing that makes this more understandable is simply the astoundingly poor design and implementation of bicycling roads, particularly in the Helsinki area. Bicyclists do not see even the road designers care about safety and legality, so that decreases their motivation to obey the rules (that they sometimes know, sometimes not).