Don't be denser, judging others by their appereance is shallow. The fact that people still do it doesn't mean that when you change your clothes that's any kind of expression proper.
It's just a cheap way to signal something that you might or might not be, and only superficially at that.
Yes, don't treat people badly (mostly) because of the way they look.
But be realistic. Someone that wears all black has made a choice just like the person that is always fashionable with lots of clothing. Some beard and hairstyles take more work than others. These are lifestyle choices people make. Someone knowing how to do 20 hairstyles to get their hair off of their neck decided to learn that instead of something else. A man with a complicated beard style probably spends some time daily on it to keep it up. A person with nails half the length of the fingers they are attached to probably eshews some practical things simply because the nails are in the way. A person that wears traditional clothing due to religion probably isn't a good candidate to date me.
I understand that being poor might make it so you don't have a lot of choices in these things. I've been there: My look was basically whatever I was forced to wear to work and whatever I could find at thrift stores. At the end of the day, though, I still had choice -and to discount what these choices tell others about you is, in itself, dense - as is discounting that humanity often makes snap judgements based entirely on how things look.
You use "cheap" as a pejorative, but it's actually a positive. By signaling that you are X, or believe yourself to be X, (where X can be anything - gender, hobbies, wealth, social class whatever) you gain the interest of everyone who is seeking X without needing to speak to them. And save the time of everyone who isn't interested in X. It's a cheap, efficient way to filter people. Is it perfect? Heck no. But humans are often happy to sacrifice accuracy for speed.
It's just a cheap way to signal something that you might or might not be, and only superficially at that.