I agree 100% with your argument, but not with your conclusion.
The present, labrynthine social welfare system already provides the state MORE levers over vulnerable people than #ubi.
Discussion
What I meant - though didn't say explicitly, to be fair - is that UBI will put almost EVERYONE in this position of vulnerability.
If UBI was more than 50% of the median household's income, then I'd agree with you.
I can't imagine that being the case, however. Typical Western governments' tax takes are no more than 25-50% of GDP, in total. And wars, whores and vanity projects eat before social welfare of any sort.
I want to see obese, spiteful, blue-haired petty tyrants driving for Uber, because UBI gave the policians an alibi for cutting them loose. I daresay UBI will never happen, because the public service is such a powerful vote-buying machine. But it is within the realm of the possible...