Realistically yes...problem is, since the default diplomatic status is war, you invariably must kill some enemy ships simply to stay alive...structures, SBs, and planets are one thing because in order to destroy those you have to go on the offensive (usually)...but with ships, you could be destroying entire enemy fleets in defense of your planets or simply to stay alive...
That becomes a problem if defensive actions have diplomatic repercussions....while maybe realistic, such modifiers would leave the military actions bonus/penalty more to chance than decision making...I can choose who I attack, but I can't necessarily choose who attacks me...
Not really sure if this should be one way or the other, but I certainly can understand why the devs would want killing ships to have no diplomatic effect...if they intended for killing ships to change diplomatic statuses, I'm sure v1.32 will fix this...
if you blow up a fleet of frigates I would think the owner should have a negative reaction.
I don't think it's just the owner, its other factions too...it'd be like America getting ticked at Syria because it attacked Israel...now, that is logical, but with these game mechanics, if Israel attacked Syria but suffered losses, America would hate Syria more despite the fact that Syria did nothing wrong (it merely defended itself)...while that may happen in reality, in terms of game balance it's just not a really good idea...