His Dudeness,
I have flown with some very professional ex GA pilots. However, from what I saw daily in an airport crammed with G, D and N registered Citations, Lears and Gulfstreams was cringeworthy and infuriating. Lining up on busy runways but not ready, causing landing aircraft to go around, taking incorrect taxy routes, taxying without clearance, pushing back without clearance, level busts, altimetry errors, entering controlled airspace VFR without clearances and generally getting in the way with ridiculous speeds downwind or on base or when taxying... yes, some airlines did it too, and no-one is beyond making mistakes, but with less than 20% of the aircraft at that base being GA but causing 90%+ of the problems, I stand by my remark.
Look up the London TMA level bust statistics and you'll see the diabolically disproportionate amount of level busts they have. Look at the amount of runway excursions they have, all because of chasing greasers. Look at how many airlines refuse to recruit GA pilots (several I worked for had that policy).
There are some extremely capable and professional GA pilots. Only a fool would deny that. But that part of the industry is riddled with cowboys.