Have you tried this? It takes forever to clean out a bucket. At the scale we're talking about, doing this on a single thread from the CLI tool means you could go home and come back the next day and cancel it then, and you still wouldn't have made a particularly big dent in the bucket. It's really a pain in the neck to delete a whole bucket full of data when you actually want to. It's "easy" to start off a recursive delete, sure, but I think you're overestimating the "kaboom" factor.

not every business critical bucket has petabytes of data in it

This one does. We're talking about Tumblr.

Maybe the moral is that you shouldn't rely on third party clients for mission critical stuff if you dont know what they do.

and also have backups like a normal competent person/organization does

I know in the particular example that is something that's good advise and more or less easily done.

Do you think it would be good to extend said argument to say scp / ftp clients?

awscli is a first-party client.

He mentioned a third party GUI wrapper on top of the CLI.

This would take so many hours to actually run though, probably weeks for that amount of data.

maybe someone at Tumblr can test this...