[59nadir]

No one needs to be fighting allocators; they are far less inhibiting and pose less of an issue than GC or RAII will in the vast majority of cases. They're far easier and simpler to deal with on the whole as well. You're always interfacing with memory management somehow and the implicit way is usually much harder to work with overall. The idea that having an allocator and explicitly working with it is for "that last bit of performance" is a bit disingenuous, you're usually losing far more than that with implicit allocation and deallocation. On top of that you simply inherently have a harder time understanding the behavior of your program.

[xigoi]

Manual memory management is one more thing to care about instead of the actual logic. With automatic memory management, you don't need to think about memory at all; what could be simpler?

[59nadir]

Easier in the best case and much harder in the worst, when your lack of thinking is an issue (which it definitely will be unless you're prepared to use more of the machine for no reason). Simplicity is not about what's easier to use, it's about how you interface with something, how simple and straight forward that interface is to use, how many things are implicitly or explicitly affected by that thing, and so on. Automatic memory management usually implies an assumption that allocations can't fail, memory is infinite, etc., so the assumptions and complications are many. It also adds more code you didn't write and have no direct control over, which complicates your problem solving in many ways.

GC or other automatic memory management is only easier if you have absolutely zero care for resource usage. RAII will oftentimes lead to single allocations and deallocations, for example, unless you take care to not have it be so, which is an immense waste of resources.

It's fine if you don't care and you know that that's going to produce slow, bad software, but let's be honest about that instead of saying you can not care and everything will be fine.