back in the day, fins used to be metal and the boards were big/heavy. My aunt was surfing 20-30 years ago and her board hit her in the kidney. the metal fin caused all sorts of internal bleeding, she almost died from it. never heard of that from a glass or abs fin but modern boards are much lighter weight
The titanium fins are very light, much lighter than glass, and the material is very slightly softer than glass.
Any fin can be dangerous, titanium is certainly no more dangerous than glass.