Blood magic?

Harmful, good and bad are a personal judgement. In the case of Blood Magic, it is because of its gruesome history and perhaps even its misuse.

You dont have to hack someone or something or even hack yourself. Such things have been done by people who probably lost the plot.

Of course, those who practice it need to be mature, experienced and knowledgeable about magic. And most of all you need a sound mind.

Please do not label the use of blood in magic as bad, just because the concept has been misused in the past and left un-researched. Several pagan rituals have been labelled with all sorts of things due to lack of understanding.