Comment by palata

> But if it's not worth $400 to me to have a lawyer write a letter, then I'm going to use a permissive license.

Again: if it's not worth $400 to have a lawyer write a letter, just don't have a lawyer write the letter! But you can still have the copyleft license... for the situation where it may be worth a lot more in the future. Or just to give leverage to fellow developers: if I use a copyleft library at work, then I can tell my managers that I must contribute my changes upstream, during my working hours.