The Joseph Rowntree Foundation (JRF) is a century old foundation that is devoted to answering a very similar question to the one you pose: what are the social evils of the day, which are the top priority and what are solutions to the social evils. The e-zine Vision attended Royal Society of Arts where the JRF Director, Julia Unwin, spoke about 21st century social evils. In her opinion, the current top social evils are affluence, avarice, alienation and anger. Unwin attributed affluence because of its affect on environmental sustainability and resource renewal. She defined avarice as greed that goes to the extent of disregarding other humans and considering them nonhuman and expendable, giving one example as the 21st century slavery of human trafficking in women and children.
Unwin described alienation as the continued development of behaviors that treat others as having no dignity or worth, as in domestic abuses and violence, and that fail to treat others with civility and courtesy--old-fashioned, but necessary, words in deed. She defined anger as the result of growing alienation breed by loss of dignity, humanity, civility and courtesy. Anger results in further destructiveness of unity (unity is the opposite of alienation), which engenders self-destructiveness and greater enmity leading to brutality and deaths (as the Internet triggered suicides show).
Audience members added the social evils of the vulgarization of society, extremism, child poverty, environmental (indoor and outdoor) contamination, and spiritual deprivation. It is difficult to choose "the worst," but if pressed to a point, I might personally begin with the twin evils (one intellectual, cognitive and spiritual, the other relating to health and quality of life) of the vulgarization of society (e.g., movies, music, magazines, teen sexuality, etc.), because it breeds alienation and anger and avaracie, and the contamination of our indoor and outdoor environment, because it breeds dignity destroying health problems, like obesity and attention disorders as current research is proving.
[Below is the link to the article about JRF's Driector Julia Unwin's speech as reported in Vision.]