Again, check the T and C of Hilton or any hotel. It will contain a disclaimer about their rights to preventing fraud. Checking ID is a way to do that for them. Terms and conditions are too long as it is, they cannot include every scenario. I think any court of law would uphold their right to refuse someone if they could not produce ID when asked. Now, whether they could keep someones refundable room charge and still deny them their stay that would be another issue, not to mention bad customer service.