eBay is not the government. They are not arbiters of what we are and are not allowed to do. Many people have sacrificed their lives to ensure that we are not governed by arbitrary tyrants that we have no say in, and it's frankly shocking that people are now like "Well, they paid a lawyer to set up a C-Corp in Delaware so I guess it's fine that they decide what we're allowed to read now".
Unless you think that businesses, schools, and families should also be prohibited from blocking pornography, or should otherwise be forced to facilitate access to eBay, your suggestion is untenable from a business perspective.
Besides this is a ridiculous strawman. "If you allow people to sell Dr. Suess books, you must therefore also plaster the front page in explicit pornography." Obviously not.
The Internet is increasingly winner-take-all and is controlled by fewer and fewer larger and larger companies. Allowing a handful of corporations unrestricted reign to dictate what we are allowed to say to each other is antithetical to a free society. Reductio ad absurdum arguments are not going to help you when cabal of corporate censors with no accountability decide to eject you from society for daring to question the intellectual fashion of the moment.
You may have identified a real problem in society, but you have not proposed a viable solution.
"forced to allow"
vs.
"prevented from denying"
Think about that difference.