By 'get along', I mean both exist at the same time together. A fork is good. Those who seek to prevent a fork are removing the most important tool of bitcoin - the ability to arrive at a concensus regarding a better system.
two networks, two chains is precisely what I propose. Let's do BU and SegWit at the same time. Get 50% of mining working on each. Then, let free markets pull miners to the 'other' chain in time as they make their bets on which will be most successful in the future. All we really need is about 25% or more of mining power to go to the minority fork prong - and then BAM! the experiment is on. May the best man win. This is good for bitcoin - bad for BlockStream.
Yes, a fork is good, depending on what kind of fork it is.
So let's do this two forks/chains/coins thing. How will services decide on what to use? If they use both, will you pay for the extra infrastructure needed to operate servers with both blockchains and integrate the new one on these services? I'm talking about exchanges, online wallets, online stores, gambling websites, etc.
How are you going to convince miners spliting hashrates evenly? That's probably even harder than getting some services to use both chains, as there's no guarantee of breaking even if miners change chains (and there you have an example of a fork that can be perceived as bad).
This is bad for Bitcoin. This will create chaos. We cannot at any given point say "let's start both these systems with even force and see who wins". It's impossible to reach an equilibrium that allows us to do that. We have to build upon what we have and see if whatever is introduced is strong enough to win and become Bitcoin.