You are right in terms of moral rationale, but what I think will matter to Putin are the costs and benefits to him of an invasion. Finding a proximate excuse will be easy, especially for a former KGB agent.
The costs will be higher and the benefits lower based on the (lack of) rationale. Forcing the Finns into Russia will be very bad for everyone involved even if successful, and failure is obviously worse for him.
You are right in terms of moral rationale, but what I think will matter to Putin are the costs and benefits to him of an invasion. Finding a proximate excuse will be easy, especially for a former KGB agent.
The costs will be higher and the benefits lower based on the (lack of) rationale. Forcing the Finns into Russia will be very bad for everyone involved even if successful, and failure is obviously worse for him.