Some of that table is already mitigated: we test blood for HIV, so transmission by blood transfusion is unlikely. Transmission by pregnancy is less likely simply because few women have HIV: 80% of new cases in the US are male, 20% female.
The real question is whether "having a conversation about prep with your doctor" is going to lead to someone caring enough to pursue a prophylactic course of medication when that same person doesn't care enough about his own health or others' to avoid risky sexual encounters. Is someone irresponsible enough to pursue causal, unprotected sex with random partners also likely to be responsible enough to visit a doctor proactively and comply with a prep regimen? Sure, it's a "really good idea," but a simpler and better idea is not to have random sex in the first place. A "really good idea" depends on a level of self-control that some people obviously lack.