It's a strain on portability. Instead of just having a C or C++ program you actually have MSVC++ program (this is actually really common) or GCC program or cla

It's a strain on portability. Instead of just having a C or C++ program you actually have MSVC++ program (this is actually really common) or GCC program or clang program. Sure one can argue that the C standard is too lax. But these kind of errors come simply from the fact that people learn C by trial and error, which doesn't work with that language. Personally as long as the compilers still allow one to enable the optimizations it's not that bad in the end. Portability issues for badly written programs remain however.