Assume that thought, emotions . . . sentience is a separate entity from the flesh. That one resides within the other, but doesn't have to. What then what do we, humanity, do when the the human body is deemed to be officially more work than it is worth? When our most intimate tool, the body, becomes an unreasonable hindrance to us, to our minds?
Can the body be upgraded by software and hardware like so much software and hardware that our computers see? Surely they can. Glasses, watches, aspirin, clothing are all hardware upgrades or patches to the body. The software of our ideas, the way that our methods of processing external information, manipulating it, and affecting our environment has changed and (i think) improved over the years.
We have no objection to discarding old theories and out-moded ideas, perhaps saving them for archival purposes or sentiment, replacing them with new, better, more efficient or more satisfying ones. Ideas are intangible and immortal to us so long as they are saved in some form, somewhere. We may have to slap a few emulat(ranslat)ors on to understand the old or unfamiliar stuff, but it can be retrieved. Still, most of the time we don't care much to revert back to an earlier version, preferring to try and debug the one we're running. It doesn't cause much grief to see software pass on, because we have the option of going back.
What about hardware? The body slowly of improves itself from generation to generation but at snails a pace compared to the 18 months usually taken for improvments in computer processing power. Related to that is the fact that we are not comfortable with (or indeed permitted to) throwing away out moded models of humans. The idea is more offensive and would cause more up roar than even the RISC v. CISC debate could.
Eventually, the time will come when an intel chip isn't good enough and it is just foolish to keep emulating older, less efficient memory models and the like when brand new software must be used. What happens when the body needs to be put aside for something new. When no new implants or prostheses can justify the performance loss that just being in flesh-and-blood incurs?
How can humanity justify or indeed motivate a change of form for our mind's most immediate tool, our bodies. Will that step be available to everyone who wants to take it?