I’m not “avoiding” anything except that I sense this thread going off the rails with yet another one of your whinings.
You made a simplistic and misleading statement about what is potentially a complicated issue, and calling water vapor a “greenhouse gas” is itself very misleading and is a typical talking point of climate denialists. And by saying “especially at high altitude” you imply that water vapor would have a lasting effect on climate everywhere, but even worse at high altitudes. This is blatantly false as the global tropospheric water budget is so enormous that artificial emissions would be negligible even if they were relatively long-lived, and they’re absolutely not.
There may be some nuggets of truth here but the significance is far from certain. The effects of contrails haven’t been well quantified, though H2 powered aircraft would probably create bigger ones, but it depends on so many other factors (altitude, humidity, and atmospheric microchemistry) that the net effect is largely unknown.
A large hydrogen economy could potentially affect methane and ozone levels and induce H2 leakage into the stratosphere, where oxidation could create H2O that is longer lived than at lower altitudes, which is potentially the single biggest concern.
Are these things important? Maybe, maybe not. These are all largely unknowns. But you didn’t say any of that despite your penchant for verbosity. You made a simple blanket statement that is simply unsupportable. And then roared at me like a deranged lion when I pointed out the inaccuracy.