It's true that the design was for unsuppressed firing with a fixed gas system.
And I get what you're trying to convey about the convenience of the forward assist when tuning an adjustable gas block. I'm assuming that you squeeze the the adjustment down on the block until the amount of gas is either shut off completely or so low that the gun will not function, then slowly open it up until the gun does reliably function. It's that window of operation where the gun will pick up a round from the magazine but will not quite chamber that you're concerned with. If one uses the forward assist to gently ease a partially chambered round home while working on this adjustment, there SHOULD be no problem, assuming that one starts with a "known good" gun with a reasonably clean chamber at the outset.
It's whenever one's use of the forward assist becomes incorporated as an integral part of the "manual of arms" and thus part of the training / practice regimen that I take issue. But as in all things "gun", it's your gun, not mine. Everone is free to operate their own any old way that "floats their boat." 'Merica!
