Well, @Old Witch is generally more technical with his comments than I am, but...
You could in theory (and in reality sometimes) not use a SERM OR taper your dosages, and still regain at least some (and POSSIBLY all) of your natural hormone production. But in seeking harm reduction, as well as optimum physical development, we aren't looking for success "more often than not", or something similar. Everything we do (hopefully) is geared toward giving each and every one of us the HIGHEST chance of success hormonally, and ability to keep what we have gained physically.
Surely, you weren't taught that, if a person's own hormones have been shut down by the introduction of exogenous hormones (or hormone mimicking substances), that weaning them off of the external hormones would bring their own production back up to where it should be just as quickly and efficiently as removing all outside hormones at once?
And, time is a factor in restarting natural hormones, as well as maintaining the physical gains that have been accomplished.
I appreciate your civil response, but I'm really not sure how our two (community's) views could be so different on this.