I certainly don't disagree with you and emphatically agree that the best way to wholesale, from an ethics perspective, is to buy it outright. Unfortunately, it's a very costly and inefficient method, and in this area, at least, it's a romantic idea. The problem with it is the closing fees involved, and your not just paying those fees once, you're paying them twice, both on your purchase and on your sale. And if you put it on the MLS, take 3% right off the top (assuming your licensed yourself, otherwise it's 6%). Sometimes those fees can outright kill a deal if the seller is refusing to come down a couple of grand to cover closing costs. But if you were able to offer a little more by entering into an assignable contract, thereby avoiding those costs altogether, you may very well now be making a deal where before, there was no deal. The seller would be happy, you'd be happy, and your buyer would be happy. It may require that you not provide a detailed explanation of how the whole process works because, let's face it, it's complicated and complications scare people. Scared people don't like to sign things. And perhaps some people feel that's not ethical, BUT, you've been able to solve everyone's issues. I think you can debate about the ethics endlessly, but the outcome is for the greater good.
The other aspect you bring up is pretty obvious. If it's a good enough deal, people will buy it. And yes, that sounds very good. However, in practice, there are many elements that make it much less simple than you make it sound. There are many, many variables that go into the value of a property. Some tangible, some subjective, some obvious, some subtle. It's not difficult at all for even the most experienced wholesalers to misjudge a property's value, for the whatever reason. I have done it myself and I have personally witnessed the president of our local real estate investor's group do it. It just happens! And then there's the fact that wholesalers spend a lot of time, money, and effort trying to find a deal. Some even pay franchise fees (HomeVestors). Sometimes (whether this is right or wrong) they get desperate because, as with many businesses, they may be experiencing a cash crunch. Desperation often leads to logic-defying behavior, such as trying to market and unmarketable deal. And then, of course, unless you're an experienced and certified home inspector, it can be difficult to know exactly what a good deal is if you're unaware of some obscure issues with the house. Unless you want to pay $300 for each and every one of your potential wholesale deals, which is just not feasible. So yeah, it's easy to say, just get a good deal and people will want it, but that's not always easy to do.