Not really – you won't get into an inconsistent state when everything is reactive. One thing that might lead to catastrophe is having cyclic dependencies, but reasonable runtime/compiler can detect those.
That's like saying "There will never be bugs".
There will be bugs.
And when you come across one and you can change a variable and have another variable affected in some other part of your program and you have no idea how these two variables are connected, you are going to have a nightmare of a time debugging.
> you have no idea how these two variables are connected
Simply traverse the reactive graph to reveal how/if two variables affect each other.
Cycles and dynamically changing bindings are still problems, but they can be tackled.