"Our sales contract is enforceable under the laws of the United States because business transactions are exempt from First Amendment rights
Especially, of course, when the company adds conditions to the bill of sale after the sale is complete.
"But the problem is the checkbox is all or nothing - either you only use Google Play, or you allow everything."
Not true you can use the check box, install your third party application and the remove the check limiting installs to play store only again.
"Who cares what phone some illiterate sweatshop worker has?"
People who make malware and want it to spread as far as possible.
Smoking is more addictive than heroin.
There are two ways to write error-free programs; only the third one works.