It is NOT legal to give your friends audio cassette tape copies of music you might legally own.
I don't know where you heard that information but it is not true. In fact, the recording industry initially balked at distributing in cassette tapes for that very reason, and tried to push non-recordable 8 track tapes on consumers <edit> which didn't fly mainly because you could not fast forward through parts of a song -- songs always had to start from the beginning -- otherwise the sound quality of 8 tracks was better than cassettes but not as good as vinyl </edit>.
After more than a decade of selling easily recordable cassette tapes (and complaining the whole time about exactly the piracy that you still think is legal), the recording industry moved to high-fidelity compact discs in the late '80s, believing that CD recording technology would never become cheap enough for the general public to use. Of course, that notion was destroyed in the late '90s (I bought my first CD burner in early '98, it was 4x, took almost an hour to burn a CD, burned as many coasters as good CDs and blanks cost more than a buck each, and cost $400 bucks), so the whole media content industry made the decision to switch to DVDs (or Super Audio discs). For now obvious reasons, that decision is now on hold and the industry is in turmoil.