$ find . -name accept_ra -exec sh -c 'echo 0 > "$1"' inline-sh {} \;
inline-sh: ./accept_ra: Permission denied
The error message tells you it's an inline-sh that fails to open a ./accept_ra file.
$ find . -name accept_ra -exec sh -c 'echo 0 > "$1"' _ {} \;
_: ./accept_ra: Permission denied
$ find . -name accept_ra -exec sh -c 'echo 0 > "$1"' '' {} \;
: ./accept_ra: Permission denied
Makes it less obvious and more confusing to the user what is actually failing to open that ./accept_ra.
Hence the recommendation to use a meaningful value for that first argument after sh -c 'code'. Repeating the command name is generally just fine. As in
sh -c 'code using "$@"' sh actual arguments to the inline script