On the other hand, making it harder to fork also gives security / stability to Bitcoin
No other hand; it's the same hand. That's what I implied. That forking is not desirable, it reduces security.
and if someone were to try coming up with a real contender, the economics (miners switching or not) will show which chain / which coin is more popular and should be pursued. In other words; it would be easier to figure out the 'winner'.
Exactly. Miners follow demand. History has proven it. For example, if Bitcoin Cash had more demand than Bitcoin, it'd probably have more hash rate than it too. It's approximately 173 times less than it.
No they don't, since the two signatures they would make for different branches would get posted to the chain as evidence [1] and their stake (a minimum of 32 ETH) would get forfeited.
I don't understand. Say you have 32 ETH, and the chain is split. You now have 32 ETH-old and 32 ETH-new. You can use both these coins with no consequences, unless it isn't an actual split, but a sidechain.