Read carefully Daniel 7:13-28 and consider the strong indication given here that the Kingdom of God will be as real and as literal as the preceding 4 beast-kingdoms (Babylon, Persia, Greek and Rome) which it will literally replace, as predicted by the 4th Annual Holyday - The Feast of Trumpets.
IMO, the agenda and impulse promoting the "within kingdom" position is due to the natural carnal desire to avoid the literal aspect of external obedience to the Word of Creator, as well as to suppress the literalness of the 7 BIG EVENTS depicted by the Creator's 7 Annual Holydays.
This matter will be soon settled by a literal fulfillment of the first Spring-Harvest Phase of the Kingdom of God on earth, as prophesied by the 2nd and 3rd Annual Holydays - The "High Purpose" of WWII - for which we have been kept free to this day. For a Talkcast on this topic, listen to: http://recordings.talkshoe.com/TC-30428/TS-902205.mp3
If the Messiah is the King of this Kingdom, would it not also be accurate for Him to say that the Kingdom, in His Person, was among or in the midst of those He was speaking to at that moment?
See: http://www.biblestudytools.com/luke/17-21-compare.html