Okay maybe its just me but Im a little confused. I will try to explain what I mean the best way I can.
If we use a "breathable" oil, then its not a sealer right?
Depends on what you mean by breathable. With the exception of Coconut and jojoba oil (and perhaps castor oil) Oils SEAL out moisture.
If silicones coat the hair, dont they SEAL in moisture like oils do?
That's a funny thing about silicones...see them more as "coating" the hair, verses "sealing" as if putting a suit of armor on each strands. They "seal" to some degree, but they also allow moisture and things in...to a degree. Get too many layers of these 'coating' the hair and then it will SEAL the hair. Where as oils, to my understanding, as long as they are not those mentioned above, will SEAL the hair until it's wiped/washed away.
If you use a heavy COATING oil for sealing, why use it for an oil rinse?
Because it'll seal in the water/moisture that showering/washing just saturated it with. If you co-washed, even better! It'll seal in the moisture from that...if you do it last (read: AFTER co-washing) that is.
Wouldn't it keep the conditioner out?
See above.
Evoo for example just sits on my hair.
EVOO is a sealing oil. I actually don't use it because I use rinses for shine. EVOO is a great hot oil treatment because it seals the hair with shine. But that's about all it does. It's slow to sink into skin at times too.
If most cones can be easily washed out with shampoo, are cones really THAT bad?
If you let them build up yes. You also need a shampoo with at least Coco Betaine to get them out or an SLS based shampoo. SLS shampoos EAT hair. Coco Betaine is not so bad, but can be drying. I wash daily (read: shampoo) but follow it up with a co-wash, then use conditioner as a leave in and my Cap n' Go method which is basically a deep conditioning treatments 7 days a week. I have no problems...however, if I stopped doing this....Things may get brittle up there.
They act as a barrier like oils do, no?
Correct. Which is why they are great for providing protection against HEAT -blowdryers, curling irons, flat irons, etc.
I read somewhere that cysomethingcone is the hardest one to get out.