Maybe the advocates of full length take so much extra fuel that they are too heavy for an intersection departure?
I think the fundamental issue here is understanding aircraft performance. The more you know about this subject, the easier it becomes to make rational decisions without relying on instinct or flying 'lore'. There is so much useful information out there and, even better, knowledgeable professionals who can explain it to those who are interested. There are several who frequent this forum, for instance.
Personally, I don't get too worried about taking off vs. runway length. If the calculations say yes and the input and output data passes a sanity check, then I go. You are departing from a known position and can assess actual conditions before making for the skies. I get more concerned when it comes to landing, especially on more limiting runways as there are too many variables: the exact TD point is unknown, as is the speed; how wet or contaminated is it? What's the braking action? Wind component? Small changes in any of these can have a large impact on the achieved landing run and a combination of subtle movements the wrong way in several parameters can increase your LDR enormously, possibly beyond the end of the runway...
As I said before, I don't think anyone should be criticised for taking full length over a possible intersection departure - it's what you're happy with. If it's costing fuel and time, however, it might be a worthwhile exercise to consider whether what you're doing is based on reason or the piloting equivalent of childhood fears. Just a thought...
