[mantrax3]

You can always shoot yourself in the foot even with a service layer.

But in a service layer you need to get it right once. And therefore if you don't, you have to fix it just once.

And coupling your business logic with your frontend layer suggests spaghetti code and violates DRY, because you typically have many frontends, but one app state.

Security is about focus. If the service coders can focus on the service being secure & fast, frontend guys can focus on the frontend being usable.

Otherwise you're asking everyone to think about everything, and human attention span, memory and skill sets are limited, and this does affect security.