I guess they don’t like the word Infantry? A marine with a rifle and pack is an infantryman, doing the same job under the same flag.
That's not what I wrote and has nothing to do with what was presented in the posted article. You are correct that traditional foot-borne military using weapons that are man-portable are referred to as "infantry" because that is how they are being employed in a military sense. However, their training for those roles are different and are for different organizations. Soldiers are in the service of the US Army, Marines are in the service of the US Marine Corps. Quite simply, words mean things and people being paid to use words ought to be able to use the tools of their trade precisely. There are too many times these days where this is not the case.
Call it a pet peeve...and people keep feeding it.