It isn't really when you consider the context. Many times when people feel like doing a re-write, it's because they don't understand the old system, or the people who wrote the old system are no longer around. Otherwise... why would you need to do a single big re-write? The old guys could just fix it up. Or the new guys could spend more time reading code.
The exceptions to this would be if you were motivated to do the re-write for a good reason, like it depends on something that is no longer dependable (e.g. Java applets or Flash).
This is in line with Naur's "programming as theory building" essay [1].
Is the system "alive" or "dead"? The system is alive if the programmers that are maintaining it have the theory of the system in their heads, and can use it to inform change, and can teach that theory to others.
The system being alive is not a property of the system in isolation but a property of the relationship between the system and the programmers who work on it.
The exceptions to this would be if you were motivated to do the re-write for a good reason, like it depends on something that is no longer dependable (e.g. Java applets or Flash).