Stripping me of one of the strongest Blood magic 'selling points' would be unfair, wouldnt it. Especially now that bloodmagic thugs are made obsolete by cheap Shishis, Zmei etc.
Let's find some way for me to compensate for these free disease demons; easiest way would be to dump them to somebody with no access to blood magic, and who isnt going to diversify into it anyway, like underwater Oceania. My blood income allows me to spam non-free disease demons just the same, trust me.
Or, I could send scouts with bloodslaves to attack somebody. This requires me to hire mass scouts though.