I vacation in Cozumel (which is an island off Cancun, for those who don't know). One of the very best diving and snorkeling destinations IN THE WORLD. I've swam with large eagle rays on a sand bar far off the coast, where I could stand up, and let the rays swim around me. I've snorkeled with sea turtles. Seen dolphins and barracuda in their native habitat (not some cage). Spotted lobster and octopus. There is literally NOTHING in the United States, even Hawaii (which has some pretty good snorkeling) which compares. If you want to dive or snorkel, then guess what? Cozumel better be on your list. I will also add that when you travel there, you can get a fair dose of Mayan history and culture, which I find utterly fascinating as it is a culture which predates European culture. The food is beyond compare to any "Mexican" food you get in the US. And, I know that you've never probably been to Mexico, but the people are lovely, family oriented, and welcoming. That's why *I* go to Mexico, and I've never felt unsafe, not even for a second. Until you've been there, you are basing your decision on second hand information, and a view of Mexican people simply unsupported by reality.
I will also repeat, for those in the back, that Puerto Rico, Jamaica, Curacao, the Virgin Islands, St Lucia, Trinidad and Tobago (probably more too....just the ones I've grabbed quickly as they get mentioned) ALL have an intentional homicide rate higher than the Dominican Republic....indeed the Virgin islands have a homicide rate 3x as high as DR. If you want to be safe, you sure as hell don't want to go to any of those terrible places, right? Mexico is FAR safer than the Virgin Islands, yet people would "rather" go there? I don't get it. Not at all. I would never discourage someone from going to any of these places, but I sure don't get the broad brush used to paint these other Caribbean vacation destinations as either "safe" or "unsafe."
Come to think of it. Don't visit Cozumel. I want to keep it easy and accessible for myself.