If you want a good argument against C it's the Heartbleed bug, a bug that exists almost solely because of someone writing something in C for which there is no good argument to use the language.
The Heartbleed bug could just as easily have been introduced if it had been written in C++. Someone who shouldn't be left unsupervised near a computer ended up writing security code that was used in everything, because "it's open source it must be good".
If you end up writing something in C with
extern myobject *alloc_myobject();
extern void func_on_myobject(myobject *x, int y);
then you should be using C++. Because if that is all you're using in terms of C++ features then the code generated should be pretty much the same.