Its not that people take issue with people actually having enjoyed Dawntrail, I think. Most people I read (exceptions always exist, people are people) take issue with their criticism of Dawntrail being attributed to "being a hater", and their valid criticisms being swatted off with a reasoning similar to "i enjoyed it so it must have been a you problem" or "enough people liked it", arguments that insist upon themselves.
Its absolutely okay to have enjoyed Dawntrail, but having enjoyed something does not mean that criticisms of said thing are automatically invalid. People criticizing the product still care, after all. And looking at the reception of the expansion, Dawntrail is definitely not ubiquitously loved.