The trick in France is, the last line often belongs to the former National Monopoly (which has been privatized since, and is now called the "historical operator"). Since monopolies are bad, the historical operator has an obligation of leasing its copper wires.

It's still bad, and we still have a relatively high barrier to entry, but it is possible. There exist for instance a number of little non-profit providers (not among the big 4), who make do by sub-leasing part of the big one's network.

There are still problems of the sort you're talking about (like "it's not us, it's the other company your data goes through"), but as people are now able to cut themselves off completely from the historical operator, their actual provider has to (and do) take responsibility, and fix the line.

As an aside, it is somewhat written in our law that to be called an "internet connection", it must provide a public IP address, and the user must be able to do whatever she wants. There are violations (Orange blocks the outgoing SMTP port), but it mostly holds: users are all allowed to host servers —though asymmetric bandwidth makes this impractical. Note that mobile connections are called "data" deals, not "internet" deals.