First, I must say giving the choice sure it would make the most sense to have every fitting welded. This assumes unlimited budget, access to a quality welding shop, the ability to do it yourself or some other method of getting things welded. I guess it would also assume you don't have any existing equipment like the most of us do. So from a purely academic stand point yes - everything welded no room for exceptions.
Now to the pointless part, let’s see if I have the straight. Person 1 has a BK with coupler or nipple on it that has threads. Person 2 has a BK with a coupler or nipple on it that has threads.
Person 1 puts on a plastic (soft) QD with a push button locking mechanism and a big plastic cross in the center of it or he/she removes the cross and possibly scratches it or polishes it as best he/she can.
Person 2 has two nice, smooth, flat stainless surfaces with a sturdy gasket in between. All can be easily and thoroughly cleaned AND visually inspected down to every nook and cranny.
Person 2 is pointless...got it.
I think you all way over state the potential problems with threads. I'll take as many stainless parts as I can get over anything plastic. You buy them once they can be abused and neglected and still bounce back just fine. If you have brass or stainless QDs you get rid of the plastic part but still have snap rings, balls and what ever else makes that mechanical connection work.
I seriously doubt there is a difference either way. I think it is personal preference and TC fittings or plastic QDs are fine. Heck, barbs and clamps are fine at our level, just not as easy to use. I'd wager a bet that most who bash TC fittings have never used one and those that defend them on the home brew level do so because they have them, like them and don't want to admit that they needlessly indulge in reckless spending because they love their hobby.
I have used them all and still do. However, I much prefer clover fittings to anything else I have used to date.
I have never been in a dairy plant but been in many a brewery. While most clover fittings are welded I have seen my share of threaded fittings. Many, many clover fittings on ebay are used and the come from dairy plants and a good number of them are actually threaded fittings. I don't think either industry has a no-thread policy...but that is just a guess.
Donk, if you have the means get them you won't regret it and i doubt you will have any problmes with this unsightly threads
The "cool points" might make you sleep better at night.