That's only if you think it's a better existence to be disassembled atom by atom and your consciousness integrated into a Reaper.
Though nothing you think is really valid prior to it happening. A change like that would completely alter your perception. Like a caveman suddenly having the knowledge of 20th century man beamed into his brain. I doubt he would had wanted it but after he has it suddenly omg, this is awesome.
Hell the reaper experience even changed Legion.
"We will build our own future! We reject the reapers!"
Gets upgrades and is 'awakened' to what it is like to be 'alive'.
"WE NEED THIS! WE MUST HAVE THIS!"
We don't really know since we never hear from those that have undergone this--all we hear is from the entity that is Sovereign or Harbinger, etc.
It all depends on your perspective. Like I said the reapers seem, given what the lore tells us, to be essentially the organic equivalent of the geth consensus. All these minds linked together to form one consensus, they no longer view themselves as individuals. Your consensus is conjoined with that of billions of others to form one entity. One nation. Go back in time and talk to your 6 year old self, I bet the person you were is radically different from the person you are now. In some ways you could say the person you were is gone since you're not the same. Yet we don't perceive it that way, you are still you no matter how much you change. You may reflect back on how much of a different person you used to be but that's usually the extent of it. You are still you, even if you think of 'younger you' as someone else. You are always you to yourself. Perhaps the harvest is not so utterly different than that. The power of perspective.
And if that's really what we become, ie Sovereign and Harbinger, then it can be argued that the process is negative because those two were huge a**holes.
It can be argued that, yes, but its entirely subjective. Again, the power of perspective comes into play. The reaper's do not view what they're doing as wrong. They are our salvation. They bring order to the chaos. Without them organics are doomed. Their actions are for the greater good of all life in the galaxy. You may not agree with this but it is how the reaper's view it, according to the lore. Once you are harvested and given all this knowledge and perspective and 'ascended' to Godhood perhaps you too would change your view and come to accept the reaper way. You will gain a new perspective and understanding. You will view it not as an limited organic with a short, pitiful life but rather as an immortal god with billions of years of knowledge and experience. You will go from being the caveman grunting at fire to the suddenly having the knowledge and complexity of Einstein.
So perhaps the consciousness is preserved but there has never been a reaper created that, when given all this insight, understanding and perspective, did not agree with the harvest. A man who is forced to view the world as round would have a hard time continuing to believe it is square. This, coincidentally, could also explains why the reapers all seem to have different personalities.
Some are a few quotes that, imo, provide relevant context to this:
“We are your genetic destiny.”
“We are the Harbinger of your perfection.”
“We are the Harbinger of your ascendance.”
“Evolution cannot be stopped.”
“Embrace perfection.”
“The reapers are more your future than ours.”
“Your species was offered everything geth aspire to. True unity. Understanding. Transcendence.” (referring to the human reaper)
Some deleted dialogue found within ME2 - granted it is deleted but it is still interesting I believe for context:
“You fight your own rebirth.”
“Thank us. Beg us for immortality.”
“You insult a future you cannot comprehend.”
“You are the one wasting lives.”
“You challenge your own ascension.”
“One must not destroy the nation.”
Honestly the more I think of the reapers the more fascinating I find them to be. Shame that the ending did so much evident damage to them.