The "joke" by Justine Sacco was this:
"Going to Africa. Hope I don't get AIDS. Just kidding. I'm white!"
You can read about it more here:
https://www.nytimes.com/2015/02/15/magazine/how-one-stupid-tweet-ruined-justine-saccos-life.html
While her family's background didn't match up with the post at all, Sacco seemed somewhat oblivious to the impact of her words on others, still working in social media PR at places like "Hot or Not" which is all about impact and judgement of others. She was also dis-proportionally targeted by someone well-known on social media, and a few others in the article above were targeted by alt-right brigades after telling the world they had experienced something in public that made them feel uncomfortable.
People haven't quite realized yet that their words brought to social media, even coming from one voice among billions, have much more power. But not just because they have the ability to communicate publicly. It's because they have instant access to large audiences who are all but guaranteed to receive and digest their words. And with these large audiences comes the risk of being misinterpreted. Sacco may have the social luxury of being able to post a joke that she thinks only an "insane person" would take literally, but it's clear that many people who post on social media really don't "know their audience".
Think about ResetEra for a moment. Tens of thousands of people may be members, but far fewer post often enough, and many more read and have read the site. For some, Era is only what they read in posts, and the multitude of other members and potential members reading are not considered, even though they (along with you) provide the revenue to keep the site going and would possibly consider joining the conversation. How many of those people feel called out when people make metacommentary about Era and its members? Do you know for sure?
As for young people voting in the US (a comment I've seen made multiple times now in the past 12 hours or so), they and their families have experienced some 40 years of slipping economic opportunity and loss of access to benefits and services, more severely and quickly depending on where they live. They've watched their families and friends made to re-up combat tours, told they are not wanted in the country, made to live on a razor's edge between citizenship and not, and seen those who have made mistakes unfairly cast as less-than human in incarceration and stripped of the right to vote. Their schools, including defenseless 6-year-olds, have been shot up without meaningful national action or bills signed into law. They've even seen a President's own party abandon him during an election (Obama, 2014). They have evidence their lives may not have a chance to end naturally. The only news media they've known continues to fuel non-truths and normalize reprehensible behavior. The results of their taxpayer-funded educations are lack of access to further education, a life of debt to gain access to further education, or vocational and healthcare marketplaces that effectively lock them out. They have no nationally-visible champions in the political arena, in the private sector, or in the populace - just a relatively scant few concerned citizens who are earnestly trying.
As for Obama's comments, it's not a matter of Obama being wrong, it's a matter of a) glossing over the practice of targeting on social media in order to cause harm, and b) normalizing "everyone's done something stupid" when NO - many people with hard economic situations or who are targets of prejudice just trying to keep afloat day-to-day do not exhibit the behaviors of others with easy economic means or social privilege who can afford to keep doing not just stupid, but sharply harmful things.
Unfortunately his comments did both gloss over and normalize. It seems to me people still haven't learned enough, or paid attention to, women who have been targeted, stalked, and denigrated on social media (and off) - things that go way beyond simply being misinterpreted. After years and years of clear examples of this, why this isn't put at the top of these conversations is beyond me. Instead it's "would you look at these people with their 'self-serving' righteousness", which is a far easier statement to make and then go no further, and allows those who continue to brigade against women to take cover behind those comments.
Obama has a real talent for making those who orbit the still-conservative middle of the US political spectrum feel better about themselves. These comments he made are unfortunately no different in this regard. It's in part how he won the Presidency, yes, but some still think that's how a Presidential election can and should be won. And yet people want young people, with all the things they experienced, to just go along with that? They want to be shown a different way to win, a way that directly addresses their experiences that have been indelibly woven into the fabric of their nation. I hope the 2020 election will be able to show them just that, but candidates are going to have to be willing to be their champion AND communicate that effectively to them. Let's see if any candidate ends up doing just that.