Flip things around: can you claim to be loyal to a faction if you regularly shoot their stuff?
I'm on the fence. If pirate factions were easier to gain standings for I'd be more interested in supporters of those factions having relevant standings.
It adds credibility but you have to take it with a grain of salt, as some newer RPer that wants to be say, a blood raider, most likely does not have the resources to run out to 0.0 and grind Blood Raider missions to back their story, and nor should they have to.
Working missions and general high-sec activities should not be a crutch or a requirement for anyone's RP.
Standings are already screwed up as it is.
Khanid Kingdom NPCs will shoot Silas in Kingdom space for sec status reasons, but I think I still hover around +9.0 standings from when I was running missions in the region. I'm not about to waste time coming up with some convoluted reasoning to explain that, etc.
Long story short use it as a backup to flesh things out if you like but never as a necessity.