Warhammer 40,000/6th Edition Tactics/Black Templars
Just because we're part of the marine codex now doesn't mean we don't still have a tactica, I mean we've got our own troops, etc.
Also, if we keep lumping all divergent lists with supplements and the like in with the main codex they spring from things are going to get bloated real fast. Black Legion and Iyanden are one thing, but between Black Templar and the rumored Chaos God specific books we might want go with separate tacticae. Similarly, we may want to make a 30k Admech army list.
(and this has nothing to do with the black Templar behind me Ignore that weak willed heretic brother, welcome to the Black Templars.
Why Play Black Templars?
Because they're angry crusading marines that threw their copy of the Codex Astartes out the airlock. They have the option to take scouts in their tactical squads and mount everyone in fucking Land Raider Crusaders. (Assuming the rumors are true.) They take the space marine dakka and give you more options for choppy while simultaneously PURGING THE HERETIC and generally not afraiding of anything. What's that, Neophyte? Bloodthirster? HOLD MY LASCANNON AND HAND ME MY CHAIN SWORD! They're a chapter, more like a legion, really, made of puritanical imperial faith and ignoring your better judgment and as such, uniquely amongst general space marine chapters, have the feel of a medieval crusading army. In space. In short, if you want your space marines to charge bolters blazing at the enemy screaming litanies of faith, play Templars. Also they wear pimping tabards.