Thank you for bringing this up! It appears ghost has this turned on by default, and I turned it off now. Sorry for any inconvenience. For context, we had an internal debate whether we should host the blog ourselves, but ultimately decided to use ghost. It ticked a few boxes, being open-source and run by a non-profit. The fact that it would do outbound link tagging by default really comes as a surprise, so thanks again for bringing it up.