Of course you can attack someone for not being in FW and question his loyality -
in character. I know, this is tricky to draw the line, but in the end 'being loyal' means doing something. Personally I prefer to have some ingame metrics/ways to do that, because only posting on the forums how perfect one is while spinning ships in the station is kind of 'meh'. Work on furthering the agenda of your given faction, and that's it. A trader trying to compete with Jita on a market might do this for his own economic benefit, but it can be also claimed that he's doing that to weaken the influence of the State on the Capsuleer market (and I think it can be assumed, that non-capsuleer trade is hot in the areas frequented by us elitist jerks, too).
In short, there are plenty of ways to paint your ingame activities into a certain light. (4TH, for example, can be validly attacked ICly, but they can also really claim to develop space to strengthen Caldari/state interests in that area for ze future.
) If you're not doing anything meaty, then you might be better off calling yourself an enthusiast and not a loyalist.