Assuming you aren’t running a charity, increasing the bottom line is always your goal. The difference between a company that burns user goodwill in the process, and one that doesn’t, is the difference between short-term and long-term thinking.

The downside with hired testers is that they are unlikely to be a statistically representative sample of your target market. I don’t think this is actually a problem for most startups or new products being launched by major players, since a lot of UX issues early in product development will be obvious to anyone who isn’t the original developers, and the number of actual users you have won’t be big enough to serve as a statistically representative sample of your target market anyway.

you can genuinely find out what message makes more sense.

explaining what your product does is hard when you’re the product expert. A/b testing ad copy helps folks parse what your product does.

If your product is actually good then having more people understand what it is, is also good.

And all of that amounts to what if no one decides to cough up money to use your product?