You seem to have no clue whatsoever what you are talking about.
'tails-autotest-remote-shell' in /etc/init.d includes a rather obvious test for a kernel parameter:
if grep -qw "autotest_never_use_this_option" /proc/cmdline
then
:
else
exit 0
fi
If that parameter is missing, the script aborts. I guess you do not know how to read shell-scripts or you did not bother to even look what it does.
And 'tails-autotest-remote-shell' in /usr/local/lib is different from the file in /etc/init.d and actually the python script called from there if needed. It also includes a pretty clear and accurate statement at the start: "ATTENTION: Yes, this can be used as a backdoor, but only for an adversary with access to you *physical* serial port, which means that you are screwed any way." As this very clearly says this is a serial-port connected remote shell, I guess you did not look for one second into the file. And if you had looked and looked at the code as well, you would have seen that it does indeed only open serial port.
So, in total: This script opens a remote shell on a serial port if you give a very specific kernel-parameter on startup.
Remind me again where there is _any_ security problem here? My guess is you are just an honor-less shill spreading FUD for money to keep people from trusting TAILS.