My opinion
In characters situations that cause someone to get angry against the realm they serve under and thus become a spy (aka - no prior OOC collaboration done and its someone you dont know OOC whatsoever) is fine
Spying and trying to RP it ingame as validation is using IC reasons as an excuse for planned OOC spying. Obviously top circumstances are rare.
I currently have 2 created by their own realm who messaged me out of the blue.
I actually had a good friend IRL of mine in DoA and he decided to get his character deported once it got entangled in war with Caligus to prevent OOC knowledge of the place.
Simply those who want the OOC spying to be ok if it is reasoned IC is the main problem. Its impossible to track first of all and its something that will likely always be in battlemaster and a problem because it is a small community and pretty much everyone knows each other so in its own place is it very hard to have IC situations where spies are not OOC created.
There are other IC ways to establish spies. For example IG I run a spy network. I constantly recruit nobles into that spy network IG. On occasion I have too many spies in one realm, and none in another. Are you saying its OOC to ask one of my agents to move to another realm and try establish himself high enough in the hierarchy to get info worth selling?