This is one of those "Mac vs PC" kinda discussions, but......
In temperatures low enough to be *really* concerned about the cold, water is *usually* frozen - unless we're talking about either a huge spill inside the shelter or possibly a torrent of water entering the shelter.... Rarely will the evenings condensation develop enough liquid to completely saturate a sleeping bag (granted, there can be saturated 'areas'...).
If someone has a sleeping bag that is so saturated with water that the insulation is compromised then they have a problem that is truly catastrophic. By this i mean to say that in nearly 30 years of winter camping and climbing i've never saturated my sleeping bag with enough liquid to compromise it's insulation - and i've made some real bone-head mistakes! Additionally, i have never met or known anyone who has. Not that i'm better or smarter than other campers (that would be a huge fib!!!!), but that it would really require alot of liquid to make that happen.
No insulation is "warm" when wet - none. I've shivered my hiney off enough times to know that wet = cold. There is no "wet and warm" unless you're talking about a bath or swimming at the beach.
The healthy, adequately hydrated, non-hypothermic human body *may* produce enough heat to "warm up" wet synthetic insulation a few degrees (depending on; How wet? How cold? How large of an area?), but if it's really wet, no insulation will retain that warmth.
If the temperature of the insulation falls below 98.2F and the body cannot warm it up, it doesn't really matter whether it's synthetic or down because you're gonna become hypothermic.
I do agree that wet down is worthless. Maybe wet synthetic is slightly less worthless. Either way, worthless is still worthless.
Besides this one primary argument against down, there are sooo many more positives to down for sleeping bags. It lasts way longer, packs smaller, has a "warmer" feel degree-for-degree, and is lighter to carry.