https://en.wiktionary.org/wiki/ignorance : 1.The condition of being uninformed or uneducated. Lack of knowledge or information.
If you had said "How could someone be so ignorant as to think that making a joke like that would be appreciated by the majority of people aware of the incident", then I'd be inclined to agree with your sentiment. My personal experience has been that when people die and it gets news coverage, most people near me don't want to hear humor.
But it sounds to me like you're equating "ignorance" with "not sharing the way I was socialized", which goes back to my point about how you come across to me as intolerant. Some cultures wear black at funerals, tell stories about how you'll meet the person in the afterlife, and cry a lot. Other cultures wear bright colors, share food and drink, and tell funny stories to celebrate the life the person lived. I personally wouldn't say "you don't treat dead people the same way I do, so you're ignorant." I'd just say "You're different."
I feel sad that you did not respond to my final paragraph. I do understand why you'd make this post and not one about Space Aids or feeding like a homeless shelter- you recently saw emotional news coverage of what happened in Florida, so it feels closer and more real to you. Presumably that's the same reason you used the word "Americans" in the original post. Not because you're prejudiced to believe that Americans are any more important than other people, but because you're [probably] American, so them dying feels closer and more real. That's a normal part of biology, sort of related to why people are generally against cannibalism or eating family pets, but are much more open to eating cows or chickens.