Re: moving functionality from the server side to the client “brings its own security challenges”.
Totally agree - validation etc. on the client is purely to help improve user experience; it needs to be replicated on the server to be any kind of guarantee that it's doing what was intended. And yep, I also agree that there are too many inexperienced web developers out there who don't appreciate that. I'm being polite and swapping "inexperienced" for "idiot" :)
We had a guy apply for a job here recently who was after £60K plus benefits, which he said was a significant pay CUT from what he'd been earning in California and London, and who could boast on his CV that he'd got experience with cool stuff like Ethereum plus every Javascript framework you could care to mention, but who had no clue how to write a secure application, nor one that was scalable or highly available. Apparently "the framework takes care of that". Knob!