They talk as if they have no worry of a coming judgment. They're not concerned about showing love to God. They believe that their purpose for living is to love people and make this world a better place to live. They reason that if all of us are stuck on this planet together, we may as well try to get along and help each other. I'm not living for God, I'm trying to live for others.
Humanitarian efforts are noble and commendable.
In fact, you can find many Scripture verses that encourage loving human relationships. And in order to strike home his point, Solomon spoke of the despair of living only for this life on a human level. We wouldn't know that the human soul lives on and faces God in a life to come. Humanitarian efforts would have no eternal value. But this love is possible only among those who know what it means to be loved by God and to love Him.