User blog comment:SeraphLucifer/Discussion/@comment-79.115.69.72-20160126210828/@comment-5619706-20160127030213

No, there were way too many inconsistencies in established lore for reapers to make sense as angels. And I mean PLENTY. I'm sorry but I don't even think the "you're entitled to your own opinion" applies in this case. There was a reason, Adam Glass and his friend were bombarded by fans in twitter when they revealed this retcon. Also, you might want to check out the following links: (1), (2) and (3)
 * Reapers were more or less neutral (at least in their early lore) and adhere to Death's advocacy of the Natural Order (In My Time of Dying, Abandon All Hope, Two Minutes to Midnight), while Angels are soldiers of God that are aligned with Heaven (beginning with Lazarus Rising).
 * Castiel told Dean that finally, for the first time in 2,000 years, Angels are walking visibly among humans (Are You There God? It's Me, Dean Winchester), whereas reapers have always been known to hunters (Faith).
 * On a related note, demons made a big deal of angels revealing themselves (Lazarus Rising) but had no problems dealing with reapers (In My Time of Dying).
 * In fact, demons like Azazel and Alastair have been trapping, possessing and even killing reapers (In My Time of Dying, Death Takes a Holiday), despite Alastair claiming he and Lilith did not know how to kill angels (On the Head Of A Pin). So why is everybody all caught up in the hubbub and hype of the arrival of angels when they have actually been tussling with them for a long time?
 * Reapers had 'sandboxes' or appearances they could change willingly (In My Time Of Dying), Angels needed vessels (Lazarus Rising). A certain 'subtype' of angel not needing a vessel completely undermines the whole apocalypse arc of Sam and Dean serving as opposite vessels to the two most powerful archangels. It just doesn't fit. Same as how Azazel managed to possess an actual reaper (or "angel"). Tessa wasn't possessing a vessel. If she was an actual angel--then a demon managed to possess an angel?
 * If reapers are angels, what does that make Death, their 'big daddy reaper' (Abandon All Hope)? The archangel of death? A semi-archangel of death? No matter how you put it, it also drags Death into the equation when they have clearly established that he is a horseman, and that the title 'angel of death' does not suit him in a literal/technical sense, because why would God create an angel that was capable of killing him?
 * Lastly, Carver's own canon contradicted himself. Why is it that when Castiel angel-proofed himself (I'm No Angel), Bartholomew had to recruit reapers? It doesn't make sense if Carver was setting reapers up as angels. That means they should not have been able to find Castiel, too, since all angels were being kept from finding him. There's just too many contradictions for reapers to actually fit in into being angels.

There were a lot of uproar because it did not make sense. I'm really sorry--I try not to be abrasive if I can help it but this is one massive bull from the latter season I could never let go.