why are acls & user xattrs off by default?

I was looking through Anaconda to see what it's doing when it makes ext3 filesystems:

        rc = iutil.execWithRedirect("tune2fs",
                                    ["-c0", "-i0", "-Odir_index",
                                     "-ouser_xattr,acl", devicePath],
                                    stdout = "/dev/tty5",
                                    stderr = "/dev/tty5", searchPath = 1)

-Odir_index is redundant by now; it's default in e2fsprogs.

-c0 -i0 are probably subject to some debate, but...

why are user_xattr & acl required to be mount options for ext3? (added to defaults or explicit?) I'm sure there is some history here, but why build it all into the module, and then turn them off without some extra magic passed in? What's the advantage to disabling user xattrs & acls at runtime by default?

Thanks & just curious,

-Eric