I’m going back to string n glue for my new SS, but I won’t use carbon bars on the single speed, I maul them to death and they all get very creaky and flexy after about 6 months abuse.
Quite happy with carbons on the 5″ boingy bike though.
As with most things, use the correct material for the right application and there are minimal issues.
also worth bearing in mind that lots of bike bits used to be designed for typical rider weights of around 12st, whereas lots of british riders are seriously lardy boys who still think a 3 lb carbon hardtail will be fine with a 20stone rider 😯