Objections are natural in any business. There are individuals who thought that making money online is just easy that it can happen overnight. When they fail to meet what is expected from a business they become critics of the program and claim that they have been scammed.
But in reality they may have failed to understand that affiliate marketing like any other business requires risk and effort. It works you just need to do your part correctly. It can also be luck that governs things at times. Generating traffic and converting them to sales is what really makes the business work.
It can be compared to a conventional business. When you put your whole heart into it you accomplish something that others may not. There are also programs that do not really give as much success as others do. It all depends on the methodology that individuals are using. Most likely the objection in affiliate marketing programs comes from people who tried but did not tried hard enough.