Poll: Do you think that Apple or Exxon brings more value to society?

Apple machines use plastic. Plastic is derived from petrochemicals. Petrochemicals are created by ExxonMobil (and other oil companies).

We may not like oil companies because they are greedy, capitalistic assholes that manipulate the system to their benefit. But disregarding the impact plastics and polymers, most of which are derived from petrochemicals, would be extremely naive. Try to imagine modern life without plastic. Just look around whatever room you are in and notice how many objects use plastic. And that is just in the consumer space of an average room. Imagine all the industrial and manufacturing processes/parts that use plastic.

“Market cap" represents a "perception of future performance", not an assessment of a company's "value to society”.

Investors are just expressing a sentiment that Apple - a company that has rebased its product and service offerings at least five time during its 35 years of existence, in many instances cannibalizing the incumbent cash-cow to pioneer a new business opportunity - may have better long term business prospects than ExxonMobil - a company that has an 100+ year history of providing the petroleum-based commodities that are the current basis of our civilization, but has arguably demonstrated no other competencies.

You're comparing apples to oranges in the worst way: It's like asking if the police or fire department is more important to a small town (answer: you need them both). I also think the very notion of the "most valuable company" is a very loaded phrase as well.