> While this is theoretically true, the reality is that thousands (tens of thousands?) of people do it every year successfully.

You are correct, but if you do it on a tourist visa, you can expect to wait well over a year for employment authorization, which is very difficult on a relationship.

Not to mention you always risk getting rejected (particularly if you posted your intention online) and then being essentially banned from entering the US.

For two grown adults with careers, it makes no sense to risk it, just take one of many legal routes (K-1, work visa, getting married outside of the US and then applying for a greencard, etc).