Historically, genealogy has had a difficult time being considered a legitimate pursuit because of the existence of rampant fabrication (aka lying) by its practitioners. Whether intentional or otherwise, fabrication is still a major problem. The proliferation of online user-created family trees has given those who are either too ignorant or too sloppy to verify information, an ample platform for their misdeeds. This would not be such a problem personally since I can just ignore the inaccurate information, if I didn't have those misdeeds of others constantly thrown in my face, as if I could somehow prevent my own grandfather's second wife being shown as his mother much less solve all the other problems online.
One of my friends, who is just getting started in genealogy, recently took the time to tell me in detail what he thought about all the problems he had found on a popular online family tree program. This wouldn't be so bad if it didn't happen regularly.
My comment about all this is that you can lie but you can't cheat. To put it bluntly, if your information is unsupported by competent citations to source material, it is easy to just assume that whatever you or anyone else has put online is inaccurate and suspect. If you try to justify your lack of support with bogus citations, it is extremely easy to determine that what you have cited is either wrong or nonexistent. There is always the possibility that original documents can be forged or doctored to support a claim, but there is usually more than simple interest in genealogy to support such extreme measures of misrepresentation.
I have been told over and again that user submitted trees are "useful" for hints and suggestions. That may be true, but how do you tell the difference between pure fabrication and reality if you are always inclined to believe that those who submitted the information did so in good faith? Just today, I had two different people relate to me how the information they had on their own family lines was proving to be extremely misleading and mostly false. What is the point of having a poorly documented and inaccurate family tree? Some people may be motivated to document their pedigree if they find that the information given to them by relatives is false, but others may be so discouraged that they lose interest in genealogy altogether.
One of the most common forms of cheating is to copy work done by someone else and claim it as your own. So the question is, how can you say you can't cheat in genealogy when people copy another's work all the time and claim it as their own? Simple, how do you know the work you are copying isn't also bogus and copied from someone else who fabricated the whole thing? If you don't verify the other person's sources, how do you know what you have? By this, am I condoning copying another's work and claiming ownership? Not at all. I am just saying that you cannot cheat your way into a valid, citation supported pedigree. Who do you think you are trying to impress and who do you think you can fool? The only way you can know that the work you are copying is legitimate is to verify it for yourself and if you do all the work to verify the facts, then using the information is, by definition, not cheating.
Am I then advocating redoing all of the work done by others? Hmm. That is a really good question. What I usually say at this point is that you have to do enough verification to measure the level of reliability you have in the work, but regardless of your esteem for the person you are copying, you cannot rely on unverified sources. Does that mean collaboration is hollow? Or do I escape the problem by simply attributing the work? No, collaboration is not dead, nor is it hollow. Can you avoid the whole problem by passing the buck, so to speak, and attribute the source? Attribution is important, but not a panacea. There is no way around the dilemma. If you copy family history information and the copy turns out to be inaccurate, you are simply wasting your time.