It would not be false to the facts, but it is not the best thing to do. Here are the REASONS we call that system version “GNU/Linux” rather than just “GNU”:

• It's not exactly GNU—it has a different KERNEL (that is, Linux). Distinguishing GNU/Linux from GNU is useful.
• It would be ungentlemanly to ask people to STOP giving any credit to Linus Torvalds. He did write an important component of the system. We want to get credit for launching and sustaining the system's DEVELOPMENT, but this doesn't mean we should treat Linus the same way those who call the system “Linux” treat us. We strongly disagree with his political views, but we deal with that disagreement honorably and openly, rather than by trying to CUT him out of the credit for his contribution to the system.
• Since many people know of the system as “Linux”, if we say “GNU” they may simply not recognize we're talking about the same system. If we say “GNU/Linux”, they can make a connection to what they have heard about.

It would not be false to the facts, but it is not the best thing to do. Here are the reasons we call that system version “GNU/Linux” rather than just “GNU”: