It seems those filters might not be doing much after all, for good reason.Google’s philosophy is to filter no more than necessary, i.e., as little as possible. Google considered adding the capability to filter other controversial content besides pornography, e.g., hate speech, anarchy, bomb making, etc. But these are much more difficult to filter automatically. For example, if you try to filter hate speech, you may filter out sites that discuss hate speech.
Parents should take care of their children.
Bicyclists should use a headlight at night.
Nothing wrong with the word "should", just with its misuse, as with anything else.