It's rather to our detraction in a way, the jibing, as I'm rather sure that an actual Xeno terrorist wouldn't carry on so. I just happen to be a bit of a clown and it bleeds over.
Besides, one can only try to be evil for so long before everyone you meet just throws *static* at you whenever you log in.
Any and all conventional missiles in addition to any and all mine layers are, of course, permitted. To the best of my knowledge there are no missiles or mines that are reserved for any specific faction alignment and those which are tied to a specific factions (I believe train disruptors are a Hessian product) are freely available to all care of our good friends to Zoners.'
Edit: It was brought to my attention that I did not fully answer the question, so here's a little more:
The reason that it's specifically Xeno particle cannons and civilian pulse weapons is because other weapons are generally considered in good taste only when acquired via diplomatic relations. I.E. Hessians may use Outcast weapons because those two factions are chummy with one another.
The Xenos, on the other hand, have zero friends. They're rather unique in this regard and that's one of the reasons I enjoy playing them. You undock and the whole world is red to you save the other fellows flying your flag.
So the end point being that the only guns we use are Xeno guns because who's guns would we use otherwise? One could say Zoner, but that just isn't good form.