And my point is...Once you've tried several offerings from a brand, you should be allowed to form a general opinion about that brand. Is it possible that you might be proven wrong? Absolutely, but that doesn't mean that your opinion of the brand is completely off kilter. I've eaten' a lot of Spam in my day. Now there's Spam light. I think it's OK for me to assume that it probably taste quite a bit like Spam.
Using your own logic, I might ask you how it is that you assume you're straight? How many men have you had sex with? Even if the answer is 300, how can you know that you just haven't tried the right one yet?
IMO certain assumptions are indeed OK. It's more about how you handle being proven wrong.