Agree with everybody else here :-)
But just on this one particular point:
"Marketers love it because it allows them to link to external content without taking the reader off the page."
This is a reasonable fear for a client to have. The user leaving the site and not being able to get back.
However, in every single usability test I've done, opening external content in a new window makes this problem worse - not better.
(If they don't want to get back to the old site - the client has a different problem. And opening things in a new window won't solve that either).
Users have a well understood mechanism for returning to a previous page. The back button. If they want to get back to the old site - they can. Opening external links in a new window breaks this mechanism.
I've seen the opening of a new window confuse and annoy users again and again. Responses have included:
- Being aware of the new window - and just being annoyed by the perceived forcing of behaviour.
- Not understanding what happened when the back button failed - and just giving up.
- Typing in the URL again when the back button failed - and having to "start again"
- Carrying on their original task on a competitor's site because they went to Google when their back button didn't return them to the original site.
- ... etc ...
What marketers really like is keeping their making sales and keeping their customers happy. Explain that opening new windows will do the reverse (even better - show it with some user testing) and you won't have a problem.