You seem to be arguing that FDR was a leftist because of the policies he implemented. But I think what you are missing is why he implemented those policies. I think the truth is he didn’t really have the public interest at heart. His agenda was to contain a growing threat to capitalism in the form of the Communist Party of the 1930s. His strategy to contain the CP was to neuter the party by bringing it into the Democratic party fold, alienating their most militant members, and slowly squashing their agenda. Of course he had to appeal to their interests to do so. But it was a temporary strategy, not a real shift in US policy. There are a few articles on the topic if you are genuinely interested. Here’s one. And here’s a quote from another.

The New Deal reforms Sanders evokes were not the product of a farsighted, enlightened reformer, but responses to tumultuous class struggles in the early and mid-1930s. These reforms sought to contain explosive social struggles and were never truly universal, excluding women and African-Americans, for example. After mass struggle ebbed, Roosevelt shifted back to his original goal of stabilizing US capitalism while moving toward establishing US global domination during World War II. Progressive reforms came to an abrupt halt in the late 1930s, allowing the rollback of many popular gains during the 1940s.

Whether humanity will survive really is an open question. Despite all the rhetoric and protests and promises the annual CO2 emissions have continued to increase steadily. It’s wishful thinking to imagine that we are going to do anything about this before the consequences of our choices force our collective hand. Any report or scientific paper that includes a phrase like ‘there is still time’ is just not accepting the reality of the situation. A year ago James Hansen published Global Warming in the Pipeline where he wrote “Equilibrium global warming for today’s GHG amount is 10°C”. A 4–7 degree rise over 5000 years ended the last ice age, Ocean levels rose 400 feet. A 10 degree rise in a century or so would be way too fast for most species to adapt. It would inundate the majority of our most populated cities. I could go on, but I get depressed writing about this.