IMHO there is a balance between the fleeter and their target. Make the moons too cheap and too big, then the balance shifts too much in favour of the defender. Remove ruby moons (or big moons) entirely, then like King says nobody is safe. Personally I think the balance is ok as is on most of the servers.
In addition, MDs are slow and very vulnerable to a ninja. Ppl don't tend to risk a lot of RIPs unless they have seen a fleet. And remember there is the chance of a backfire - I have seen it happen, 5k RIPs disappear (my only complaint about that was there was no df, as I recall, now that would have been sweet!!).
Ways to fleetsave even if you have no ruby moon - 1) keep your fleet hidden and don't let anyone find it 2) FS to a 9.9 inactive or alliance moon.
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