It's considered unsafe to edit
.config because there are
CONFIG-options which have dependencies on other options (needing some to be set, requiring others to be turned off, etc.). Other options aren't meant to be set by the user at all, but are set automatically by
make config (resp.
Kconfig to be correct) depending on architecture details, e.g. availability of some hardware dependant on architecture variant, like an MMU.
.config without using
Kconfig has a high chance of missing some dependency, which will either result in a non-functioning kernel, build failures, or unexpected behaviour (i.e. the change being ignored, which usually is very confusing).