It's not for entirely malicious reasons. Those super chargers run at very high watts (250 KW) in some cases and people with hobo repaired batteries could cause some serious fires if they could just plug into the chargers.
Tesla does need to have approved vendors at some point, but I definitely understand their logic in blocking access.
Tesla disables supercharging for any totaled vehicle, as they want to reduce the likelihood that a Tesla catches on fire at a supercharger and they're put on blast on the news for the next week.
