What a snide reply. Is it necessary to be a doctor to have an opinion on healthcare policy?

They were speaking of medicine rather than policy, and getting it wrong. PReP is not the same course as treatment, and prophylaxis is always a thing given to healthy people rather than sick ones. The side effects are considered manageable: you watch for signs of liver problems and you don't give the drug to people prone to them.

I'm not a doctor but I can read the prescribing information[1], which they don't seem to have done.

[1] https://web.archive.org/web/20161221124917/http://www.access...

Arguing the facts is totally good. And you may very well be right (I don't know anything about the subject). But attacking the commenter's position because he/she is not a doctor (like you are not a doctor), struck me as poor form.

You're correct about that. I apologize.

Would you feel comfortable as a layman arguing with people who have been studying the topic for a decade about the tradeoffs involved?

Of course. In many circumstances, the experts don't even agree. It's incumbent on me to inform myself, and I can lean on those very experts, but I'm not at all comfortable ceding how to weigh those tradeoffs to the people who identified them scientifically.

I'm not necessarily saying you ought to cede to the experts, I'm saying you ought to do the research they have already done if you expect them to take you seriously about changing the way they do their jobs.

Obviously it's not breaking any laws to post an uninformed opinion on the internet, but what is going to be accomplished by it?

Attack the message, not the messenger.