Exactly 

 it is a core principle of signals intelligence that once the message goes over an untrusted channel it is likely captured

but that still doesn't stop people from respecting this anyhow

it's one of the benefits of a network protocol like LN, it isn't broadcast so the chances of a delete request being respected are higher at being successful on such a channel, the majority of channel rebalances are discarded after they are no longer able to be applied