In theory, sure, a disinterested regulator would ensure that the cost of polluting was higher than the cost of not polluting. (Another solution to this problem is via property right enforcement, by the owners of the nearby polluted properties that share airspace/water table with the polluter).

But in practice the EPA is hardly a disinterested party when it comes to publishing studies on its own cost effectiveness. It exists to increase its budget and scope, just like all other agencies, but has no check on its behavior. Its officials are not elected, cannot be fired, and are effectively invisible to the public. Moreover, opposition to EPA malfeasance/corruption is often caricatured as opposition to clean air and clean water itself.

As an example of regulatory pathology, consider that the EPA is giving grants and instruction manuals to NGOs, telling them how to sue the agency into expanding its powers.

m.yahoo.com/w/news_america/epa-funds-greens-sue-221700941.html?orig_host_hdr=news.yahoo.com&.intl=us&.lang=en-us

  The EPA even tacitly encourages such suits, going so  
  far as to pay for and promote a "Citizen's Guide" that, 
  among other things, explains how to sue the agency 
  under "citizen suit" provisions in environmental laws. 
  The guide's author — the Environmental Law Institute — 
  has received $9.9 million in EPA grants over the past   
  decade.

  And, to top it off, critics say the EPA often ends up 
  paying the groups' legal fees under the Equal Access to 
  Justice Act. 

  What's going on? "The EPA isn't harmed by these suits," 
  said Jeffrey Holmstead, who was an EPA official during 
  the Bush administration. "Often the suits involve things 
  the EPA wants to do anyway. By inviting a lawsuit and 
  then signing a consent decree, the agency gets legal   
  cover from political heat."

Most people have never read an expose on the EPA; they think of them as the "good guys" who protect us from the evil polluters. What's funny is that we can see through this kind of logic when the normal police invoke it to justify any action in the pursuit of common criminals, but not when the environmental police do so -- and the EPA is most certainly a branch of the police, with the power to raid, fine, and seize property.