A gold dragon in the Eberron setting is not always lawful good. We could easily be up against a gold dragon - either it is neutral or evil and has plans that need to be thwarted, or it is good but is taking actions that need to be stopped. Alternately, we could simply be tricked into fighting it (like in Running with the Devils).
Personally, however, I consider silver dragons to be more fearsome foes than gold dragons, as in a world where Clerics can always have Mass Restoration (and soon Mass Heal) prepared, a paralyzing breath is far more dangerous than an Str-damage breath.