I CAN'T GIVE YOU SCRIPTURE FOR SEXUAL FANTASY BECAUSE THE PHRASE NEVER APPEARS IN THE BIBLE.

If you treat the Scripture as authoritative (as I do) then hopefully you'll see a big problem with making doctrines with no Scriptural basis.

A dictionary definition of lust is interesting but not very practical from a theological view point.

My questions are what are Scripture's concerns regarding sexual purity? and does having any kind of sexual thought violate them? (Again, see my theological study linked in an earlier post.)

"You're the one comfortable handling things. I'm the one who suffers guilt from it... ;-)"
I'm not saying I'm completely comfortable "handling things" yet... I'm still exploring and experimenting.
One thing I believe strongly however, is that God doesn't want us going around feeling guilty all the time about something that is part of our created humanity, given to us as a blessing to enjoy. I suspect much of our guilt on this subject is imposed by moralizers and wanna be do-gooders rather than based on good theology.

I also object to the line of reasoning (I'm not putting this on you btw Empire) that acknowledges the need but says, "oh well, we will fall and God forgives us and we get back up and keep going".
Whilst this statement is true, the "oh well" inevitability of falling is a mockery to God I believe. If this is a problem that CAN'T be overcome... then maybe its not MEANT to be overcome. Otherwise... hurry up and bloody overcome it for crying out loud!

Blessings
Cat.