KillerOnion,
I do agree with you, when you say that anyone should be allowed to carry around a banner that says F*** Bin Laden. This is, well freedom of speech but what I would also say anyone is allowed to carry a banner around saying 'I Love Bin Laden'.
Its a difference of beliefs be it religious, media driven or just plain fanatisism it is an individuals belief.
So I think if someone wants to have a Swastika on their gun, let them. They may have it there to make a point, they may be racist, they may just think it looks cool, but until you approach said person and ask why they have it there, you'll never know.
Therefore after you've asked them and presuming they answer your question then by all means make your personal judgement on them.
Just to point out, though I addressed this to KillerOnion originally as it was his comment i was commenting on this isn't directed to anyone inparticular from the sentence begining 'Its a difference of beliefs.....'
Loki