Even if Ainsley would be haunted by the idea of consuming human meat, he was so okay with eating beef raw. After getting a go-signal from the doctor, Sinclair got Stuart to serve Ainsley with meals using raw meat. Not only Steak Tartare was on the menu, but there were more of those that only needed meat and a few seasonings.
It was a harmful practice, but Ainsley had a dragon heart inside him. It could naturally use the bad things he might catch into strengthening his immunity to them. As for producing his own poison, that was quite unheard of from any who shared a dragon heart. Moreover, Sinclair didn't wish for him to develop his own poison.