#4 seems like a zealous overgeneralisation. JOINs get a lot of crap.

Yes, it's no secret that large joins on huge amounts of data can often be very intensive. From that does not follow, however, the exhortation to simply avoid them categorically. That's a little too much blanket statement for me.

For instance, joins are often used in situations where there is a numeric type column that refers to a very small table of enumerated values that have a textual or other translation, and there is a need to produce the latter in a single query. There's nothing wrong with that join from a performance standpoint, even for very large values of n.