to what extent is there a regulator on Steemit to prevent spam, copyright infringement or porn etc that may create income for those users but damage the community for others?

@steemcleaners pretty much handles copyright and spam

porn is 'regulated' from the NSFW tag.

and of course anybody can use the flag to "adjust" the community as they wish.

remember, not even steemcleaners is a "regulator" but an independent body that was formed from a large number of people in order to solve specific problems that were a major concern from all.