Re: Why no tsuba?
I don't think those who are justifying the use of tsuba are doing so because it offers a "cheat" or easy way out to any exercise or technique, which some are categorizing as "bad practice". The example of somebody going for your wrist and using the tsuba to block it is too limited. If it were that easy maybe the attack or the exercise make no sense in the first place. The tsuba is there, but that's not all that's saving you, imo, except of course when the technique specifically calls for using it -- but that's not what's being argued I believe. Exchanges are often far more complex than that, and sometimes in the middle of a move a weapon might slide towards the hand (I find it happens often against jo) and the tsuba is there to protect the fingers. If we had to slow down and tone down the power to bring those "mistakes" down to zero… it's honestly not worth it, and besides the point.
Like Keith said, real swords have tsuba. There is a wide variety of armored combat situations in classical weapons. I'm not an expert, but the reason for tsuba in some bokuto might be a combination of historical and practical reasons, or maybe it's as simple as having the practitioners use something that resembles the real thing (which have tsuba). Anyway, before making sweeping statements about whether to use it or not I say first consult experts on what is best for what you're trying to do.
How would you draw a sword inconspicuously without a tsuba? Consider that sword work might start with the sword in the scabbard.
Consider that the tsuba might work for you or against you. What can happen at different ranges?
Another thing to consider is how a practice weapon vs. a real weapon behaves on contact. Wood vs. wood, wood vs. metal, and metal vs. metal bounce, deflect and absorb power in completely different ways. Then you have wood weapons tapered with metal against these options. Have you tried all of the these? How is tsuba involved in all these cases?