I'm not sure exactly what you're asking. Firstly, it's a type error to say "taking equity out of the service via profit". Profit, by definition, does not come from equity. Secondly, the government should spend public money to build public infrastructure because that's one of the major purposes of a government. Thirdly, if you're saying "private companies will use that public infrastructure to make profit", then I guess, yes, they will, just like they use roads. But I would certainly say that if water companies sell water from public reservoirs to customers then they should be required to pay for that service! Why not?

They're saying that using public funds to build out private infrastructure is a huge transfer of wealth from the public to the rich, and if the subsequent profits of that investment disappear into the same private pockets (or even abroad), the ROI calculation becomes so unfavourable that there's no sound financial reason to invest. There's a huge difference between investing in government-owned infrastructure vs privately-owned.