Will non-Muslims burn eternally in the Fire even if they had good morals and had engaged in humanitarian activities?

Answer

Whatever Allah Ta'ala will do with non-Muslims, will be His prerogative. It will be subject to His Mercy and Justice. We cannot fathom the mysteries and wisdom of Allah Ta'ala. Your ideas will not influence Allah Ta'ala. It suffices to believe that only Muslims will go to Jannat, and that kuffaar are doomed for everlasting perdition regardless of their good deeds which are not structured on the Foundation of Imaan. The Qur'aan describes their good deeds as mirages – phantoms - devoid of reality and substance.

Your brooding over the issue will not change the condition of the people. You are plagued by shaitaani wasaawis. The only way to combat these shaitaani thoughts is to immediately lapse into Thikr. Don't brood over the thoughts. Just divert your mind to Thikr. Recite Istighfaar and Laailaha il lallaah constantly when afflicted with these satanic thoughts. The thikr will, Insha-Allah, eliminate the thoughts.