Sulfates are in most shampoos and they're very drying, so they can make hair frizzy, dry, and coarse. That's especially true on people with curls, since hair oils have more trouble moving along the curly strands than straight ones. The drying factor is the argument for giving up shampoo. But if you give up sulfates, you also have to stop using silicones. Silicones are in a lot of conditioners and styling products. Silicones work by coating the hair, and many of them can only be removed from your hair by sulfates. (If you stop using sulfate-based shampoo but continue using silicones, you end up damaging your hair because the silicones build up.)
I gave up sulfates and silicones in September or October. My hair has gone from frizzy, dry, messy curls to nice, soft curls. I still use shampoo once a week, but it's an organic sulfate-free one. The rest of the time I use a light conditioner as my co-wash. Your hair still gets nice and clean, but it's because you do a hair and scalp massage with the co-wash, effectively using friction instead of sulfates to clean the hair. I'm sulfate/silicone free due to dryness, so I follow the cowash with a heavier conditioner and leave it in for a while.
I'm not sure how all of that compares to the WEN stuff, but it has been working really well for me. I've gotten more hair compliments since going sulfate/silicone free than in the 5 years before.
Darcy--I have no idea how (or if) going sulfate and silicone free would work on someone who can't condition. Many conditioners have protein, and protein weighs down superfine hair. I wonder if your problem with conditioners is the protein or if even protein-free conditioners would be too heavy. I don't think that sulfate and silicone free are the way to go for everyone. I've switched myself and my curly-haired 3 year old (whose hair was terribly dry and coarse pre-switch), but I still use sulfates and silicones on my 6-year old. He has straight hair that isn't bothered by them.