The only way a person can be held blameless for contracting an STD is if they were married & faithful to their partner. In this case, a person can reasonably assume that their spouse is also being faithful. Although this is not always true (thus the transmission of STDs within marriages), it is again reasonable to expect it.
In all other cases, people are directly responsible for their sexual behavior! One can not & should not depend on someone else to prevent them from getting an STD.
In all other cases, people are directly responsible for their sexual behavior! One can not & should not depend on someone else to prevent them from getting an STD.