fewer companies does not mean less competition. charter and TWC operate in virtually exclusive areas. The only real competitive difference if this were to happen is... a name change.. that's it.
ISPs wield more market power against other network providers and content owners when they get bigger. a merger here consolidates the bargaining power of TWC and charter and has immense potential to hurt consumers even if they weren't ever going to operate in the same cities.
There's really no need to. Basically these are internet providers at this point, and there are typically a number in any given area.. The (formerly) phone company, the (formerly) cable company.. the wireless companies.. medium distance wifi services.. on top of that federal regulation requires the companies owning the copper and/or frequencies to allow others to buy capacity over those systems and resell it. tl;dr if there was actually an ability to compete in a segment, companies already have the ability to do so because of this regulation.. that they don't is a pretty strong statement on exactly how thin margins on the market are.
this is false. POTS service providers have to resell capacity to competitors, but DSL/fiber/cable/wireless providers do not. back in the early 2000s DSL companies had to lease their lines out but that requirement was killed by the FCC in 2005.
even with the common carrier decision that the FCC made recently to bring back their net neutrality rules, local loop unbundling is specifically not being forced on ISPs.