This has been covered already on the first page of the thread - the site you recommend uses highly questionable "diagnoses" in order to recruit people whom they convinced to join. The so called "self-assessment" includes leading questions, manipulative language, intellectual dishonesty and so on and so forth. Plus, the questionnaires on such sites are worded specifically so that MOST people would come out with a negative label.

There are psychological tests that are validated on millions of people, such as the Millon or MMPI inventories. This kind of thing is pseudo-scientific to put it mildly. Plus, when you get tested using REAL tests (the ones that have been vetted and validated through and through and developed by real experts - even those tests are not perfect though, but at least they offer the best available option), the psychologist doing the assessment, more often than not, is not a treating psychologist and thus has no interest ($$$) in the outcome. You go to a testing psychologist, go through a battery of tests, the psychologist read your results, interprets them, and provides a writeup FOR your therapist. The testing psychologist receives a one time honorarium for the assessment and then bye-bye. The treating therapist develops a treatment plan partially relying on the psychological assessment results and partially relying on knowing the client and on what the client wants. In that setup, both that the tests have been validated on millions of people and that they have a lot of very similar questions which ultimately gets as close to the truth as possible, AND the lack of the evaluating psychologist's monetary gain from giving the client any kind of labels or diagnoses provides for the most objective assessment possible. Not perfect, no, but as objective as they get. Finally, on real psychological tests, you get to learn where you stand with respect to the whole population of test takers.

Here, the self-assessment told you that you are a self addict, whatever it means. What about others? Are you the only sex addict? Are 90% of other people who took the test also sex addicts, whatever it means? And if the latter, is it really a disorder if 90% of users have it? And what about self-selection - since you happened to be on that site where you took self-assessment, you self-selected as someone who thinks that he is a sex addict.

This is just a very brief list of shortcomings of such "assessments".