I don't agree. The "existing infrastructure" you speak of consisted of obsolete technology in both switching and the local loops. It worked fine for POTS and low speed dialup but it was no good for higher speed work. The phone company had to invest in new facilities to support broadband. This investment was done in a competitive marketplace.
The cable companies had to compete against plain old rabitt ears, high gain rooftop antennas, and satellite TV.
Obviously rollouts in different areas occured at different times. But generally consumer broadband service was offered on cable and phoneco at roughly the same time.
No, it is not. FIOS is treated differently. It is more difficult for the phone company, but I suspect they chose this path to avoid regulations.
I still maintain that the capital cost to lay fibre optic, esp when it can be done selectively to areas with the best customers, is not unsurmountable. The cellphone world was supposed to be two companies, but quite a few have built networks, and quite a few more sublet services from those networks.
I understand what you're saying -- since Verizon FIOS is deregulated, they can do as they please, just as any other business may require exclusive packages with their customers. (I don't think a nice fancy restaurant would appreciate it if I came in, ordered only a cup of coffee, and then ate a pizza I brought in with me.)
That is a problem with deregulation and the marketplace. There is no guarantee there will be competition. Sure a busy corner _might_ have three supermarkets involved in a price war, but could just as easily have only grocery store who charges premium prices. That's the way it is in a lot of markets in a lot of industries. There is no way around it if you want deregulation and a free marketplace. That's how it works.
There is nothing stopping the cable company or a new business from laying their own fibre or whatever network and offering their own service, undercutting Verizon's FIOS prices. If Verizon FIOS is priced so unfairly high, someone else should be able to undercut them (presuming there is a demand by customers to use their own ISP.)
The other alternative is to go back to regulation and control the prices. Then we're back to the old Bell System.
As to ISP's, I expect a consolidation of them because of a variety of factors in the industry.