there is actually such strong evidence
What evidence? PUAs may use a lot of trial and error in developing their techniques, but do their tests count as valid experimental evidence, or just anecdotes? Where are their control groups? What is their null hypothesis? Was subject selection randomized? Were the data gathered and analyzed by independent parties?
Would you accept this kind of evidence if we were talking about physics? Would you accept this kind of evidence if we were evaluating someone who claimed to have psychic powers?
One of the reasons this topic is of interest to rationalists is that it is an example of an area where rational evidence is available but scientific evidence is in short supply. It is not in general rational to postpone judgment until scientific evidence is available. Learning how to make maximal use of rational evidence without succumbing to the pitfalls of cognitive biases is a topic of much interest to many LWers.
Followup to: Do you have High-Functioning Asperger's Syndrome?
LW reader Madbadger uses the metaphor of a GPU and a CPU in a desktop system to think about people with Asperger's Syndrome: general intelligence is like a CPU, being universal but only mediocre at any particular task, whereas the "social coprocessor" brainware in a Neurotypical brain is like a GPU: highly specialized but great at what it does. Neurotypical people are like computers with measly Pentium IV processors, but expensive Radeon HD 4890 GPUs. A High-functioning AS person is an Intel Core i7 Extreme Edition - with on-board graphics!
This analogy also covers the spectrum view of social/empathic abilities, you can think about having a weaker social coprocessor than average if you have some of the tendencies of AS but not others. You can even think of your score on the AQ Test as being like the Tom's Hardware Rating of your Coprocessor. (Lower numbers are better!).
If you lack that powerful social coprocessor, what can you do? Well, you'll have to run your social interactions "in software", i.e. explicitly reason through the complex human social game that most people play without ever really understanding. There are several tricks that a High-functioning AS person can use in this situation: