In writing an argument supporting reading this novel, I would focus on the timeless and universal themes the novel conveys. On some level, Ethan ultimately lives a miserable existence because he finds himself trying to follow the rules of society instead of following his own heart. The novel also shows how isolation, both physically because of the town's bleak possibilities and emotionally in his marriage, can destroy a person's hope of living a fulfilling life. Ethan first tries to escape Starkfield, an incredibly symbolic name, by going to technical college. He is forced to return following his father's death. Later he finds himself isolated with Zeena, caring for her in a loveless marriage. His isolation cuts him off from the hope of any sense of personal fulfillment, which supports the theme of the great need for encouraging, stimulating human companionship.
I'm not generally in favor of arguing against reading anything, so the second half of this prompt is a bit tougher. If I was forced to come up with reasons people might steer clear of Ethan Frome, I'd probably lean toward the issues of immorality in the work. Ethan Frome is married to Zeena, so his escapades with Mattie lean toward adultery, at least emotionally. Perhaps he should have first ended his marriage to Zeena before becoming so emotionally intimate with Mattie. The double-suicide attempt near the end also would leave some readers uneasy, particularly in a culture where teenage suicide is on the rise. If pressed, I might argue that teens (if that is the intended audience) should not consider how a man's desperation leads him to consider and actually attempt to end his own life.
I hope this gives you some ideas to consider for both sides of this prompt. I'm linking to the eNotes page for other themes in Ethan Frome to help you consider other areas of support for your analysis.