We definitely get too tied up in tiny differences, but it isn't all bullshit either. I think there are at lease three real issues where the cheap vs expensive argument means something.
- Safety and Reliability. Better steel, quality manufacturing, and good design result in knives that you can count on to work as intended. Cheap knives are more likely to fail in unexpected ways. Some of those failures can injure you. Some of them may leave you without a working knife when you really need a knife. These are low-percentage issues, but the consequences can be significant.
I think of it in terms of buying a motorcycle helmet. You aren't all that likely to need it, but if you do, a good helmet will get you through with less serious injuries. The classic advice is "go ahead and get a $20 helmet if you think you have a $20 head".
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Knockoffs. Intellectual property is often abused, but there are both ethical and practical reasons to allow people to benefit from their innovations. A lot of the cheap knives out there are knockoffs of best sellers that earned their positions honestly. Buying knockoffs makes the originals more expensive. They make it harder for quality manufacturers to stay in business. And they discourage good design.
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Happiness. It is worth noting that many of us pay more for a good knife just for the satisfaction of owning it. Carrying things that make us happy, even if they don't have practical advantages, is not meaningless.