Forks are necessary. Just like a vote-of-no-confidence and new elections in democracy, or revolution in dictatorship, or Civil War if everything else fails and no consensus if reached.
Let's look at open-source forks history:
1. OpenOffice -> LibreOffice (95% users and devs migrated)
2. XFree86 -> Xorg (100% users and devs migrated, after license change)
3. Emacs editor to XEmacs (30% migrated), old fork still has advantage. But for editors, consensus is not required.
4. Glibc to Debians glibc (70% migrated), Debian +Ubuntu. The forks are compatible.
5. GCC compiler to EGCS to new GCC compiler (100% migrated, old maintainer was fired from FSF "Free Software Foundation" by Richard Stallman, the neck-bearded old man, that does endless loop in 8 steps. Old maintainer refused to accept new Intel Pentium optimization patches and didn't move his ass).
6. Linux Kernel has mini forks all the time, like Xen kernel, OpenVZ kernel, real-time, hardened security kernel and openSUSE AppArmor kernel. No major forks in horizon, which means it is well managed. (99.9% users use the standard Linux kernel, with small optimization/bugfixes by distro). Xen and AppArmor patches upstreamed into standard Linux kernel.
7. GDB, GNU debugger, had 400 forks in the 90's, which were all merged back into new GDB. (100% migration)
In short, forking is part of the open source community. What matters here is not just the code, but the community that stands behind it. I was also scared shitless when I heard, that XFree86 project ceased to exist. I feared no Red Hat Linux desktop anymore, but little I know, that Open-Source projects do not really die this way. Later I realized, that Red Hat (and others) would not allow X11 desktop to fail, as long as there is demand for it, even if among Linux developers. In the end all development continued under the Xorg umbrella, and XFree86 project died.
Open-Source projects can only die if there is no maintainer / no big demand among users.
In case of Bitcoin, old BTC, we will receive 1 new BTC and 1 new BTX (Bitcoin XT), and community will decide which is the best. Wallet backup is compatible. As long as there is community, it would have value. But temporary crash is possible due to panic selling. Long-term damage is unlikely. (assume a dude with an ancient physical Bitcoin or an old wallet backup falls asleep for 10 years, and wakes up in 2025 - his Bitcoin, or Bitcoin XT will probably be worth more. ) So, I don't believe in chicken little and the sky is falling mania-depressia. Open Source history teaches us a solution.
We can discuss those examples of ancient forks in detail. I studied it few years ago.
Best wishes,
-"Technologov", Open-Source community member. 23.07.2015.
Disclosure: I vote for large blocks. Let's try to reach consensus in Bitcoin core, and if not -- I vote for Bitcoin XT.
P.S. Read more about Open-Source forking history:
http://www.dwheeler.com/oss_fs_why.html#forkinghttp://linuxmafia.com/faq/Licensing_and_Law/forking.html 
Because Ubuntu developers started to change it into some form of stupid person linux that should be so easy to handle that everyone can do it. Only problem was that professional users didn't even find how to change their settings anymore.
Neither one of those points can be used to correctly compare with Bitcoin, unless you think OpenOffice can be put into the same bag as Bitcoin (just because both are open source). 