By default, the scanning of PUPs (potentially unwanted programs) in the Real-time Shields are off. Why is it like this, who would want keyloggers? 
(Or can avast detect keyloggers and such without that checked?)
It doesn’t refer to keyloggers per se. A lot of perfectly safe things can be detected as PUP’s and I’m happy that it’s not turned on by default. Having said that, I do have it turned on but the default action is to ask since not everything detected will be bad.
Yeah, some want keyloggers on their pc. Doesn’t mean it wont detect a malicious one.
No harm in it being disabled by default but if you feel you need it just enable it.
Martin.-