I think that any ISA designer who believes that omitting from the ISA the means for detecting integer overflow is a good idea deserves the death penalty

Given that the C standard (C99 §3.4.3/1) declares integer overflow to be UB which means the compiler can and often will do anything it damn well pleases with your code, I can understand why the RISC-V designers, under the influence of the stupidity of the C standard, could leave out overflow detection. I'm not saying it's a good idea, in fact it's complete and utter braindamage, but I can see where they got it from.