It is well understood by most people on these message board, that when we talk about "IP" in the parks we are talking about the use of an existing IP as opposed to developing an new IP specifically for an attraction. Using an existing IP can become problematic if it needs to be "force fit" into the attraction or park.
My problem with IPs is how they seem to be using them recently. Imagineers are given a specific IP, and often a park or even a specific attraction, and then they must make the IP fit. I would rather the Imagineers be told what is needed in a specific park, say for example a new thrill ride in Epcot, and they determine what is the best fit whether it be an existing IP or something new. Balance is a big part of the problem now, everything needs to be tied to an existing IP, Imagineers aren't getting the ability to come up with totally original ideas.
I actually don't have a problem with using outside IPs. I still remember when I first heard Disney was teaming up with Lucas to create Star Tours. I could only imagine what amazing things would come out of Disney applying their magic to the Star Wars franchise. Of course at this point Disney should have little need to go outside for IP's since they already own everything.