Rules of the air!
"I might be missing something but in class D airspace, if I am flying a B737 and some **** in a glider or microlite gets in my way "
..... errr...who's way ?
The Rules of the Air Regulations 1996 (Statutory Instrument 1996 No. 1393) - Section IV - 17 (2), suggests that being bigger, smellier and noisier doesn't mean that you have right of way-
"(i) flying machines shall give way to airships, gliders and balloons"
Now, I accept that in practice, if I see a big Bong hurtling towards me, I'm not going to insist that it's my right of way to the point of a loud bang.
On your training point, I'd suggest that some glider pilots may possibly have less formal training than a PPL. Some will have the same and others will have considerably more...Indeed quite a few glider pilots fly airliners as well. Whether this makes then better qualified to dial in a few digits and press a button I'm not so sure about.
A key issue with transponders is that gliders don't carry enough power to run a transponder. Some gliders don't have ANY onboard electrical equipment. Mind you, it does mean that the carbon footprint is rather small!