Perchance I shall lift a line from Shakespeare, to inquire of Oxford if the words hath been used or abused. Embarrassment likely shall follow.

In my not Shakespearian example of can not, I stand behind the usage for emphasis, rhythm, and the fact that the object of shame is “not be stopped”. “be stopped” by itself has no meaning.

Remember, this is NOT entertainment. It is only to be read by people who really want to. In the 4th grade we were shown a film about the Russian Revolution. The teacher started this film, and left the room. The narrator droned on about how there was so much hate, both sides wanted not only to kill, but to disfigure their enemy. On the screen, dozens of people were being lined up and shot multiple times in the face with rifles from very close range. I was horrified by my classmates, who were drooling and cheering in a very bloodthirsty way. These were real people after all, and NOT cartoon characters who were being killed. Children need to learn something about courage and character, before being exposed to bloodthirsty stuff. Alerted by the noise, the teacher returned, and immediately stopped the film. It was all a big mistake; it was the wrong film. It’s a crying shame hate can not be stopped so easily.

The answer from Ask Oxford is quite easily interpretable as an endorsement of Alex’s view. The Washington State University Language site is not even a site endorsed by the University but one professor’s home page. In the citation of the historical use of cannot it looks like an evolution toward cannot and it could be quite easily argued that “can not” (literal) is not used in single one of those cases where it means unable too. The one place it is cited is a fine example of how vague that construction is without some context.

Alex is quite simply correct here.

@TheSongFrog:
Although I am not a native speaker, I dare get rid of both errors below:
“I can see not only the cottage but the dock as well.”

1. If the obvious error you are referring to in your example sentence is the use of “cannot”, you would write the sentence with the words separated as “I can not only see the cottage but the dock as well”, agreed? In that case, why couldn’t you replace it with “can’t”? “I can’t only see the cottage but the dock as well.” Another example, “I can’t only sing, I can also dance.” It may look or sound unusual, but technically it is not wrong (it’s the contraction). Therefore, if you can use “can’t” you can logically use “cannot”, whether you think it is lazy, ignorant, common, or whatever your opinion. Though as I said, I do believe “can not” is a better choice for this type of sentence.

2. You started your post by saying people come up with reasons to justify their beliefs without any factual basis. Where is your “factual basis”? You said yourself that “either form is correct for casual or ‘common’ writing. For professional or formal writing, however, [you] prefer ‘can not’ as the actual correct form.” Preference is not a fact or a form of proof. You can stick with what you were taught, which is completely understandable and not incorrect. But every one is taught different ways by different people, so the method you were taught also does not serve as proof. The authorities say both “cannot” and “can not” are acceptable, but “cannot” is usually preferred. So if you insist on using “can not” instead of “cannot” in the context of “can’t” because you think it is more formal or professional, it could actually be counter-productive because it is not the accepted use, and could cause confusion because the reader is trying to distinguish those instances that “not” is followed by “only”. If we can’t go by what authorities or style guides tell us, then what proof is acceptable?