Dark Matter should be returned to gathering points.

[Catharsis]

You are right.
SE should fix the Active Help text.

In every city, in every camp there is a NPC selling Dark Matter for cheap.

Grade V Dark Matter is 350 gil per piece. It is often cheaper just to use the Repair NPC than to purchase Grade V. We have 11 or 12 gear slots (depending on the use of the offhand) and repairing all of those would cost 3850 or 4200 gil, which I do not think qualifies as "cheap".

Well, it's not so much a problem for Legacy players such as ourselves, with large gil reserves and Dark Matter stacks to fall back on; but I can see this being a great issue for people on new servers.