It'd be great if Horror authors would agree to donate a pint of blood for every one they spilled on the page.
A nasty wound? That's one donation to the Red Cross.
You fridged the lead's girlfriend? How clever. That'll be six pints.
Most phlebotomists I've talked to recommend donating only once every two months. At two pints, that's only one literary murder per year. You'd have to make it count.
Alternatively, for humorous Horror writers, it's ten thousand paper cuts per year.
Another alternative would be putting your Horror novel on layaway. You've just got to kill five people? That's going to take you almost five years. Of course, some authors strive five years in writing a good scare, so you could earn your way to your body count by the publication date. Heck, if your publisher drags its feet, you may have a few pints of credit by release, for that sequel.
You may, however, resent the laws of Horror sequels being bloodier. You may buck convention to save yourself a few pricks and cases of lightheadedness.
Blood donation is something more people would do if they thought about it. It actually does save lives, and every year some region has blood shortages. In my case, I didn't do it regularly until this year. Why? Pure ignorance and laziness. I never thought about it, despite seeing ample footage of public shootings and having friends who worked as EMTs. I deserve no quarter for not getting around to it until a blood mobile literally parked in front of my hotel.
Feel free to write a story about a blood mobile pulling up in front of a hotel. Anyone could climb out. The outcome, though, may cost you.