That is an unbearable simplistic view.
A great soap needs to have a good mix of oils (or fatty acids!) that bring certain properties to the finished soap. Do unsaturated oils have a place there? Some would say no, others would say yes.
It's controversial almost for sure, but I wouldn't think it's simplistic. I agree with everything you say here, and I am simply taking a stand on whether a certain fatty acid and its associated oils should have a place.
I think we must agree that certain oils and fatty acids do not have a place in soaping. If you make a soap with any significant amount of fractionated coconut oil, the caprylic (C8:0) and capric (C10:0) fatty acids will teach you an unforgettable lesson in what drying soap actually feels like. Plus it will smell funky. (ETA, ask me how I know. :smile: ) And being a linolenic (C18:3) oil, linseed oil is good for making varnish, not soap. All you have to do is paint it on something and oxidation will make it polymerize into a plastic-like solid before your eyes.
So all I'm doing is proposing adding C18:2 to the list of fatty acids that makes soap worse instead of better. CTAnton provides us a great practical example of some of the reasons for that.
I think we can easily agree that oleic (C18:1, as in olive oil) is useful for soap and linolenic (C18:3, as in linseed oil) is not, and that this leaves linoleic (C18:2, as in soybean oil) potentially up in the air since it's right between the two. You may say that it's useful, I may say that it's not and oils rich in it should be avoided. Of course, the proof is in the pudding and we reach our conclusions by trying it. I'm sure people cheer experimentation on this board.
However, there is a huge thing we're missing as crafters, which is objective standards for evaluating soap quality. Sometimes we talk about a particular quality of soap, like drying the skin, and everyone is talking about a different thing that they are interpreting as drying or not. Not everyone knows what to look for.
With that one it's actually simple because there's a specific way to test for it and everyone can learn what it feels like and how to evaluate whether a soap is drying. Other qualities might be more difficult to conceptualize and test, like skin feel after using a soap, but out there in industry they find ways to evaluate that.
That lack of standards makes it difficult to discuss things like whether linoleic oils are useful in soaping. I don't mean it as a criticism to say that the lack of objective tests makes a certain amount of self-hypnosis inevitable. If there is a certain belief in the community, everyone will tend to perceive it. (ETA, it's human nature.) Thus, whether soybean oil is "conditioning" as a soaping ingredient can be an impossible discussion.
Which interestingly brings us back to Crisco. It used to be that in the candlemaking community, it was common knowledge that you could add Crisco to container wax to improve its properties and help the candle throw more scent. Lots of people did it and spread the information. Now nobody does it. Everyone looks back on it as a silly practice that makes candles smell strange and give off soot while burning.
