Paleo and PUFAs
Safflower oil is mostly polyunsaturated fats (PUFA) with only small amounts of monounsaturated and saturated fats. We generally try to keep PUFAs to a minimum in our diet because they are inflammatory and extremely unstable when exposed to heat and light. This means they are liable to oxidize, and consuming oxidized fats tends to lead to oxidized cholesterol in our bloodstream. Oxidized cholesterol is dangerous because that is the stuff that latches onto the insides of our arteries, causing inflammation and plaque build-up.
Omega-6 vs. Omega-3
To make matters worse, the PUFAs in safflower oil are entirely omega-6 fats. The Standard American Diet (SAD) is already much too high in omega-6 and low in omega-3 fats, largely due to the prevalence of oils like safflower oil. Omega-6 fats are inflammatory, where as omega-3 fats have anti-inflammatory properties, so we need to make sure we consume at least as many omega-3 as omega-6 fats, if not more.
Mark Sisson laid out the problems with safflower oil in this post.