Since this is actually my research area, I thought it would be good to give some input here. Part of the controversy is simply due to the language used.
1) "Whitespace" is used in two subtly different senses by people that causes some confusion.
A) From the perspective of the potential new user of the spectrum, a "whitespace" is where the band is clean and so it could be used to deliver relatively high data-rate without having to put out too much transmit power relative to the desired range.
B) From the perspective of the existing user of that spectrum, the above perspective is troubling since it seems to ignore the externalities imposed by interference to others. The existing users' perspective is better captured by the idea of a "spectrum hole" that reflects where a new user could safely transmit without significantly bothering too many existing users. However, spectrum holes are also called "whitespaces" and this causes confusion.
The apparent weasel words "significantly" and "too many" above reflect a real set of engineering-tradeoffs underneath that must be navigated at least partially at the political level.
2) "Interference" is used by people in two different senses and this also causes confusion.
A) Interference is a purely technical concept that describes how performance degrades for a receiver with the introduction of additional signals into the environment. Here also there is some ambiguity because of a distinction between what would necessarily degrade performance even for an ideal or well-engineered receiver and what is feared to degrade the performance of possibly poorly designed or shoddily built receivers.
B) Interference is also an English word that encompasses uses like "you're interfering with my business model by offering a competing service."
Keep this in mind as you read any general articles about this subject. There are real tradeoffs involved in this topic, but sometimes the language used obscures or obfuscates them rather than making them clearer.