It is possible that curves are not linear. That is, it is possible that doing 1 of a thing is good, while doing 1000000 of a thing is bad. Your argument is the same as "you say you need water to survive? But what happens if you're trapped in a giant fish tank with no air pocket?" It is not a good argument.
You're absolutely right - human sentiment is always linear. If somebody likes eating pizza, they love being forcefed pizza 24/7 until their stomach explodes.
