Market segmentation is widely practiced. I believe your objection is not to the overall practice but rather certain aspects of it.

My local grocery store has a senior discount on Tuesday mornings.

Many places have student discounts.

Some places offer a discount if you buy in bulk.

I used to be a book store club member, which would give me a discount on prices. A local history club has monthly public talks, with discounted prices for members. And of course most grocery stores have that sort of scheme.

My father worked for a company which offered family discounts to its employees.

You'll find little support for making all of those illegal.

Of course some of these schemes are illegal in some areas, such as a bar offering discounted drinks for women, but those fall under civil rights law, not customer protection.

I tried to come up with a solid way to prohibit the market segmentation practices you don't like, but it's such a slippery concept that I failed.

Like, consider how some regions require bars to close by, say, midnight, but members-only clubs are allowed to be open after hours. These clubs respond by making membership trivial -- show up at the door, apply for membership, and you are in.

"Do you want to apply for the student club? Membership is free, with student id, and then you can pay the student club fee rather than the public fee." Repeat with "retired club, with proof of age" and "frequent buyer club', etc.