Honestly, if they're going to bring up the notion of obligation I'd think there would be at least an equivalent obligation to bring an alt to a GM fight that could meaningfully add to the battle.
Why even take the time and effort to get a L4 to the Ada battle anyways? Plant an alt at the location, maybe a leveled alt with some decent powers capable of assisting. My L50s that don't see much play any more, I plant their flag on the Ada platform and I rotate through them for 16 merits as time permits.
But I don't mind folks leeching for merits, a rising tide lifts all boats and all that, its just that one needs to be extra-careful when throwing rocks while in their glass house. There just isn't much room to stand on "obligation" here when they were going to add nothing to the experience themselves.