Marker describes the original item used in the first years of paintball because they were used to mark trees or livestock with oil based paint in forestry and farming.
Note that Daisy marketed, (and still markets), these as paintball marking guns.
We don't use marking paint so its no more an accurate description then a gun. We play a game of tag, so if you did't want to use gun then tagger would be as apporpriate.
It is a politically correct term that was used in the 80s and 90s to distance paintball from gun fanatics. Especially in America due to their Victorian style double standards of pro Army but anti gun, (obvously outside of the pro gun lobby which was also part of the distancing)
Though the US were distancing from guns by using the term marker at that time, teams still had the most violent names.
In the UK we have had incidents that have wanted paintball distanced from gun nuts, but not to the degree of the US.
Alongside distancing from gun nuts tournament paintball was also pursuing mainstream TV etc and distancing itself from the woodland gun fight point of view.
As far as the law is concerned they are guns, and there is no legal problem with paintball guns - only the appopriate use of them and that they fall within firearms legislation as air gun, air weapon etc and no licence/certificate as long as it is not legaly considered a lethal.
e.g. Get hold of and shoot any of the PepperBall range (Illegal in the UK), or other similar items rather than paintballs,and it will no longer be a legal paintball gun but an illegal firearm.
(It does not have to shoot bullets to be a gun/firearm in the UK, its based on lethalityin the various items of legislation)
In the tournament circuit its more likely to be called a marker, but that is still a PC term.
If people think just calling it a different name makes any real difference then they are just burying their head in the sand.
Outside of paintball people do not know what a marker is, its a gun.
A lot of people want to go out and play paintball and shoot their friends. Shops list guns because thats what people will look for.
Common sense says to not shout about guns all over the place, but guns are legal. If you have a valid use, will store it and handle it properly and aren't disqualified from a licence/certificate if required, then you can have one.
People happily use laser guns, spray guns, grease guns etc, gym queens get their guns out at any opportunity. Only paintballers (and firearms specialists / non artillery weapons instructors) don't like the word gun.
The anti gun crowd are equally be anti marker, if they knew what they are.