Because if you're OK with investments from capitalists, plus RoI, being paid back by "the taxpayer" (not how it works, see MMT), then...
... why are you so horrified by public debt, ie loans from capitalists, plus interest, being paid by the same "the taxpayer"?
The interest is probably lower. More importantly, unless the state defaults on public debt (which can't happen unless it becomes a "failed state"), loans don't require the public to give away any ownership of our infrastructure.
(2/2)