Not being entirely certain where you draw the line between exploitation and reasonable use, I would suggest a few things.

Those who package for a reasonable fee and acknowledge the source of software they use I do not believe are coloring outside the lines. Building a business using nagios doesn't truly seem to be pillaging the open source community, considering logos, screen, etc. are left intact or reasonably so.

In a weird kind of way, even out and out exploitation probably benefits the OS community in that it gets the software used and seen. People who work for such an organization likely take the name "nagios" with them to other jobs and spread usage in that way, some of which probably benefits nagios directly.

The problem with all of the OS licensing is that license violations when prosecuted revolve around damage actually done. Such damage is expressed in monetary units. It's hard to show damages when the software is free.

None of this is to say that it is ethically or morally proper, or that those who do so are not a bunch of scumbags. They are. The question comes down to a simple "what can be done" and "how much energy must be exerted". As well as, "what damage actually has been done?"

I got into an argument with the founder of GNU early on when the license stated you had to release all source using gcc to the open source community. I told him he could get double damages in a law suit. 2 * 0 = 0.\

In the beginning, Open Source (GNU, as it was in the beginning) was highly socialistic environment almost reminding one of commune living. It may be a nice illusion, but in reality, in order to thrive in the world, things need to be commercially viable. Benefits even from the most egregious abuse means that the author's names become well known and this benefits them.

Open Source needs to allow for commercial use in order to be viable, else it's just a shared grad project.