You state that your friend is "one of the smartest people I know." Sorry, but you need to expand your social group. 
Anyway, how much background in ASL does this "smart" friend have? Is he Deaf or CODA, has he taken a course in ASL linguistics? "Smart" people don't use such terms as "retards" to describe people. Personally, I think he is blowing smoke.
Real language does not require a written form. What about all the undeveloped nations that have thousands of tribal dialects, with no written forms?
ASL definately uses tenses, as with the spatial "time line" (backwards = past, forward = future, close to the body = present).
Is it "hard to get points across" in ASL, or is your friend just not fluent enough to do it?
