Off the top of my head... both can be used for enjoyment (I was going to say pleasure, thinking of the pleasure a shooter might feel at getting a bulls eye, but thought people might get the wrong idea), both can be used to hurt other people (I'm fairly certain more people have been hurt via sex and human relationships in general than from firearms - though obviously we are talking about emotional pain rather than physical pain, discounting the physical pain an STD can cause), both require choice (otherwise it is rape), both can kill (thinking of diseases like HIV in the case of sex), both ideally should require education, both require protection, if your SO is a screamer both might require ear protection, etc.