What would be the detrimental effect of using smart pointers?

Oh i didnt mean that smart pointers were bad or detriemental. Or even that any of the other gazzilion features of C++ were bad (or detrimental) on their own. Just that C++ has sooo many features that i dont think there is any one in the world who knows who any one feature X interacts with feature Y so your ability to reason about what you have written in C++ is significantly lowered.

If you can say I will only use features A, X an Z of C++ and some how enforce it then you are mitigating a lot of the risk. IIRC Carbon (Google's new lang to migrate their code off C++) came about because they themselves used C++ in a very bounded way (I recall a lot of the templates they created for their use of C++ actually resembled how Go code looked like and may have been one of the reasons for creating Go). But I am not sure how many mere mortals have that kind of tooling and discipline to limit themselves?

Unclear, not explicit ownership.