Even the difference between a middle initial with or without a following period/full stop will create a duplicate person, if the clicker is not careful.
Copying from another tree is never a good idea, IMHO, but I think many subscribers only look at the wiggly leaf, not at the underlying information. Many have no clue that they are copying from another tree, rather than from a valid source.
As the hints algorithm has become looser/fuzzier/whatever, there are more and more junk hints. I am a very careful researcher, and I see (and ignore) MANY hints that have no connection to the family I am researching. How many members actually take the time to review at that level of detail?