Warhammer 40K Tabletop XIX: "Understand the gravity of the situation."

[Voidhawk]

And honestly when i think about it then it makes me want to yell at those sniveling marine covards who used to play marines, but quite when the going got tough.

Eldar and Tau players have been stuck with an almost obselete codex for the most of the last 8 or so years, while different marine armies have been reigning supreme.
And when then finaly the meta shifts around and they are no longer kings of the hill, then they begins to desert in droves

Don't shout at them, and definitely don't convince them to stay. What they're doing might actually convince GW that it's strategy is moronic. Probably won't of course, but you never know.