+1 on open source projects forking freely. That’s what GitHub is all about, and it is a great thing for Open Source — no question about it.
Note however, Bitcoin blockchain is not just an open source project. It is a socio-technical system, more like a “country”, with various stakeholders participating in the real-world value exchange. There are many people who are not developers or into open source at all, whose assets are locked in that “country”. A much better analogy would be to say: “People need to get used to the idea of countries splitting into smaller countries.” Sure, this has its benefits, and often, is inevitable (see former USSR or former Yugoslavia). But, there would be something lost if USA split into 40-odd smaller countries, wouldn’t it? There is always a trade-off between ‘being united’ and ‘splitting up’. It is complicated, and unlike ‘simple’ open source projects that can freely fork, die, and re-merge the best parts in the course of time, splitting “countries” carries more weight and often results in real-world casualties.