Then the body becomes overworked because of an overflow of Jenova cells, mixed with Sephiroth's will. One would not need to remove all the cells in order to cure a victim of Geostigma.
Cloud is also a special case due to being a 'Sephiroth Copy'; his body is intimately tied with Jenova cells in a way that Geostigma victims probably aren't. For this reason, I see the possibility that Aerith's rain did not seep into every molecule of Cloud's body and purge him from all remnants of Hojo's experiments.
How do you "cure a will?" Sephiroth's will is his personal desire from his mind. He
willed the Jenova cells to become destructive, and harm people. Just like he "willed" the headless Jenova body in the Shinra Building to wake up, kill people, and escape. Sephiroth willed the Jenova cells to become harmful, thereby killing victims via Geostigma and powering up his Negative Lifestream.
If Aerith's cure was only a matter of removing Sephiroth's will, how was Cloud cured of Geostigma before he confronted a fully revived Sephiroth in AC? He specifically states "Your Geostigma's gone... That's too bad." If the Jenova cells were still part of Cloud's body and somehow "removed of his will", he could easily just will those cells with his mind/spirit to become malignant
again, thereby reinfecting Cloud with Geostigma. If destroying the will that made the Jenova cells dangerous was the only way to stop Geostigma, it would only have been cured with the defeat/death of Sephiroth. But as shown by Aerith curing Cloud BEFORE his confrontation with Sephiroth, it's clearly cured by removing the biological element completely. Not to mention that S-E states that the real main issue behind its biological cause is the Jenova cells themselves. If you don't have Jenova in you, you can't get Geostigma.
Cloud was injected with Jenova Cells as a Sephiroth Copy but he isn't
like Sephiroth, where he literally HAS Jenova DNA mixed into his actual genetic makeup. He was born completely human and had alien cellular matter introduced into his body via injection. By magical means, that foreign substance has been purged by his body.
Again, I see your reasoning. But it seems odd then that no official source would state clearly that "Cloud is cured of Geostigma and thusly purged of all Jenova cells forever, ending his legacy as a Sephiroth Copy", since that would be kind of important.
I just gave you an official source. It said that Geostigma is basically caused by Jenova cells harming the body, and in AC we learn that the reasons the Jenova cells are somehow malignant now, is thanks to Sephiroth's evil will working from the Lifestream.
We see in AC Aerith cures Geostigma. And then in DC we see that those who suffered from Geostigma and were
not in Edge, still carry the cells but
aren't dying or sick from it anymore. Because...Sephiroth is no longer around.
I don't know why every piece of plot or fact has to be parsed in a guidebook or something, when by just simple observation or connection, the answer is just obvious. There's no ambiguity or confusion about how Geostigma is cured. Aerith's holy water purged the foreign and evil substance from the people of Edge suffering from Geostigma. It's cured.
I'm sorry if this upsets you Mako, but I will stay on the "undecided" camp here until I find the official statement I am looking for.
Then you're gonna stay undecided forever because no such statement exists or will ever exist. Certain obvious elements are just not going to be stated. You're not going to find an official statement that says "Bugenhagen died and Red XIII didn't tell everyone because he found the pain too hard to bear at that time." Or "Marlene sensed Aerith's presence during the ending of FFVII due to Aerith having a special bond with children." It's just...kinda obviously shown/stated.