It's better of society if people do the right things for the right reasons, not because there's a threat of the law hanging over their heads.
Most regulatory laws come from chronic & rampant abuse. The fantasy land of free market ideology assumes that all important information is knowable & understandable in an instant, when that is rarely if ever the case. It also overestimates the power of a boycott or that a company will even understand that they're being boycotted or why.
What if all the disabled people in a town took their business away from Cafe A that didn't have disabled access & go to Cafe B. Given that Cafe A is extremely popular with non-disabled people, they eventually get enough money to expand. They buyout Cafe B, remodel w/o the disabled access & now there are no cafes that are disabled accessible. Has the market failed or has the market basically said "you don't matter disabled people, suck it".
It might be better, but it's not realistic. You might be surprised at the amount of violent crime that doesn't happen because of the law.
And the free market dynamics are just not effective in cases such as for the disabled. It may not be financially possible for a small company to cater to disabled customers -- this is why the law usually requires a business of a certain size. But once you hit a certain size you can afford to accomodate the disabled.
Now you're saying that a big company can say, "We don't allow disabled access", but small companies who may want to target them may not be able to afford it at all. So now you have a situation where the disabled aren't served at all because the big companies won't do it, and the small companies can't afford to.
I agree I'd like the market to sort it out instead of law, but I don't think it's realistic. Consider access ramps/elevator requirements for example - if a fairly significant chunk of key businesses (say supermarket, banks, workplaces, transport) in an area don't all have them, the area becomes practically uninhabitable by people in wheelchairs.