I don't see anything wrong with someone selling a product that extends the functionality of a free program. You're not forced to buy it, so if you can't appreaciate the work that goes into KK-Menu, don't use it.
What
is preposterous is this attitude that programmers should give everything away for free.
Perhaps you could write a program that rivals KK-Menu, and give it away. That'll teach 'em.
The fact that is no other docklet that does what kk does, causes me to suspect that it must be quite a bit of work to code.