This is the conservative argument for UBI - liquidate social security and distribute the proceeds; do more good with the same money because we don't have to pay means testing overhead; smaller, less intrusive government as a bonus.

The reality though is that every single social security program has been put in place as the result of a tough political fight. That politics isn't going to go away with the introduction of UBI. There will be demands to keep or reintroduce each and every social security program that currently exists. Funding can't realistically come from this source.