Can you help me choose an interesting topic and thesis for a sociology paper on Karl Marx's views of religion? My paper needs to take his ideas and attempt to apply them to a particular phenomenon, institution, social relationship, or contemporary controversy. My topic must relate to society, as this is for a sociology course.

Karl Marx largely saw religion as a way that the bourgeois tried to appease the proletariat or working class, as he famously referred to religion as "the opium of the people" in "A Contribution to the Critique of Hegel’s Philosophy of Right" (1843). Marx believed that the upper classes used religion to promise deliverance and happiness in the afterlife that the working class would never receive in life. By calling it "opium," Marx believed that religion provided a temporary and ultimately harmful release from the real problems that the working class faced, and he wrote that "the abolition of religion as the illusory happiness of the people is the demand for their real happiness." In other words, religion provided a happiness or joy that wasn't real, and Marx believed people should fight for real happiness.
There are several sociological concepts today to which you can apply Marx's ideas of religion. For example, drug use (and abuse) is widespread today. Drug overdoses now kill more Americans than car accidents do. People turn to drugs for many reasons, but there is no doubt that the same issues that Marx identified that caused people to seek out religion (suffering and material privation) make people turn to drugs. The states with the greatest numbers of drug overdoses (West Virginia ranks first, followed by New Mexico; see the link below) are among the poorest states. Your thesis could be that people who are suffering from poverty often feel like they have no future and turn to drugs as a way to express and relieve their suffering, as people in Marx's day turned to religion.
White supremacist ideology is another example because it's like a religion (though it's secular). This ideology takes people's minds off their real problems, which are also often caused by poverty and alienation from society, and gives them a convenient target for their anger and isolation. Your thesis could be that white supremacist ideology is similar to religion, as it is an expression of the pain of people who are alienated from society and who relieve this alienation in ways that do not truly help them.
https://247wallst.com/special-report/2016/06/24/10-states-with-the-most-drug-overdoses/3/