Earlier quoted context omitted.
The problem is not adherence to some constitution (especially the American constitution which contains quite some arbitrary and outdated things), but basic human rights. A constitution can be a legal framework for basic human rights, but many are pretty bad at that and the US has actively decided to not honor human rights (not accepting rulings of the International Court of Justice, the International Criminal Court,…
What things are outdated? It's a document that outlines the principles of separation of powers and the role of government. I think it is still very much relevant. Even if it was rewritten how would it be improved? Wouldn't we end up with the same principles just maybe worded differently?
There are several references to things that don't really apply anymore today. No matter how you might stand on the issue of the right to bear arms, the reference to militias doesn't really fit into the context of today's times.
[1]: https://en.wikipedia.org/wiki/Mixed-member_proportional_repr...