Maybe I'm just bad but I usually bacon the tank I'm not healing and have the other healadin do the same on my tank to create a redundancy safetynet.

There are a lot of good ways to use the Beacon. I usually put it on my primary target and heal other people, but lots of people put it on a secondary target or themselves and heal the main tank. Whatever way works for you is good.

Armor has no effect on magic damage, which most raid-wide damage or healer-affecting damage is, discounting stuff like cleaves I guess. The example in question (Blistering Cold) would not be mitigated by armor.

Yes, Beacon lets paladins basically cheat and heal both themselves and the tank at the same time. As a shaman, I can, will, and have eaten stuff, died and popped back up. Some people say only baddies who plan to die take Improved Reinc to be able to ankh every 15 minutes; I say shamans who have to follow a tank around even if it means getting puked on by a big ugly boss sometimes have to die, and its good when that isn't a deal-breaker. Our first BP kill, and our first BQL kill both, I died, popped back up, and tried desperately to keep everyone just above dead until we killed the boss (and I had pretty much given the tanks up for dead the very second BQL dropped that first time). I don't usually do it INTENTIONALLY though, mostly because it wipes out my mana and makes me semi-useless. I have intentionally let DPS die many times though, because sometimes I just can't save everybody.

Mmmmm....tank bacon 8)
I usually bacon my eggs or my toast BUT sometimes you gotta do what you gotta do and bacon that tank up.

The answer is simple. Trust your other healers. Safe yourself from potentially lethal damage.

Your comments about popping divine guardian and saving yourself being seen as a baddie makes me wonder just what kind of tools you raid with. Give me the players who will safe themselves any day of the week. If all the healers are having to move to safe themselves and the tank ends up eating it, then there's other problems. Positioning, bad luck, bad players, something.

Your first priority, regardless of your role in a raid is to stay alive so you can continue fulfilling that role. If doing so means the raid wipes or someone dies, then so be it. That will point out the problem and you can avoid it next time.