Your example exposes the flaw in the "destroy everything instantly and painlessly" pseudo-solution: the latter assumes that life is more suffering than pleasure. (Euthanasia is only performed -- or argued for, anyway -- when the gain from continuing to live is believed to be outweighed by the suffering.)

I think this shows that there needs to be a term for pleasure/enjoyment in the formula...

...or perhaps a concept or word which equates to either suffering and pleasure depending on signage (+/-), and then we can simply say that we're trying to maximize that term -- where the exact aggregation function has yet to be determined, but we know it has a positive slope.