I suspect the real argument anti-welfare people want to make, but are too cowardly to state explicitely, is: "if the poor weren't forced to accept shitty jobs to survive, we would have to pay them fair wages and/or improve working conditions, which would reduce the wealth going into our pockets."
The corollary to "if X has what they need to live they won't work" is "the only reason X works is to not die".
While on a high level it can feel that way, especially at the lower rungs of society (where people get the worst kind of jobs). But ultimately humans have a lot of motivations for doing things.
Unfortunately many people cannot act on these motivations because they are too busy trying not to starve/get evicted/die from illness. A world where no one has to worry about these is something we could all work towards.