[justizin]

Brooklyn Fiber is a commercial provider, so buying access from someone like them is basically how an ISP becomes an ISP.

If you were sharing your Cable or DSL, you might run into issues with your contract.

In both cases you would have to be prepared to handle abuse complaints, or your IP space would likely just get blocked from large parts of the internet, or at least major services.

For instance, the administrator of an office network may receive DMCA complaints about employees downloading movies or somesuch. If these continue, at some point your internet provider will terminate your connection. The same would be a concern for anonymous internet sharing.