Begin a billionaire is not inherently unethical. It's about how the money was acquired and how it is spent. This notion that it is evil is mainly a western one.
The slavery it permits (yet heavily restricts) is different than the one in your head that europeans and americans engaged in, so that's a straw man. Sex slavery is not permitted.
When you read history, you would see that many Mawali were scholars, and you can read about the Mamluki empire. This was never seen anywhere in human history.
As discussed elsewhere in this thread, the slavery that you're thinking of is still permitted in capitalist america, not to mention other forms that exist today in broad daylight, but are more subtle, so people don't say anything (and those are prohibited by Islam).