Do the obsessive thoughts that still sometimes haunt me, and the misfortunes or humiliations that follow them, indicate God's wrath upon me, and should I fear that I am among those with diseased and doubtful hearts whom the Quran mentions?

Glad tidings to you for the departure of the whispers. Be diligent in expelling thoughts by engaging in the remembrance of Allah, seeking refuge from Satan, avoiding solitude, and frequenting mosques and the company of scholars.

As for what you are experiencing, it could be a trial or an expiation for sins. Its cure lies in adhering to acts of obedience, abstaining from disobedience, increasing supplication, and consistently reciting the prescribed invocations for seeking refuge.

Do not debate with atheists except after gaining proficiency in knowledge. Be keen on advising the general public and encouraging them to do good, and on urging intellectuals to learn and act upon the revelation.

Whoever you are unable to debate, direct them to those who can, among those well-versed in knowledge and da'wah (Islamic propagation).