So for the same reasons:
- No one should fund your child birth because of your personal preferences.
- No one should fund your ER visit because of your own personal preferences.
- No one should fund your mental health care because of your own personal preferences.
Where do you stop with the personal preferences? Sexuality? Being transgender? Choosing to skydive? Ending up in poverty? Having sex? Abuse victims living with depression and anxiety? Paying through the nose for the same private insurance as you?
I am not suggesting the above are personal preference, but some people use arguments that they are, and that people should be denied healthcare treatment because of it.
Your insurance is covering a lot more than you spend on healthcare, that's how insurance works (and makes a tonne of profit doing so). A lot of people take pharmaceutical drugs to keep themselves healthy, PrEP is one of the many.
I'm fully aware of the side effects, I'm one of the few who had a severe allergic reaction to it, that was a hellish few days I do not wish to repeat; but I'm still for people who can take it being prescribed it if it helps reduce risk.
As for cost, maybe the patent system needs an overhaul, or maybe drug companies should have the same price for all customers, or perhaps healthcare should be centralized and and the current dictatorship of insurance and drug companies reduced to mere socialism instead, but that's a whole other discussion.