The Universal Basic Income proposed by the Left is different from that proposed by the Right. Rather than replacing the welfare state it is a supplement to it.
As Srnicek & Williams note in “Inventing The Future”, 2015 (p.297):
The conservative argument for a basic income – which must be avoided at all costs – is that it should simply replace the welfare state by providing a lump sum of money to every individual. In this scenario, the UBI would just become a vector of increased marketisation, transforming social services into private markets. Rather than being some aberration of neoliberalism, it would simply extend its essential gesture by creating new markets. By contrast, the demand made here is for UBI as a supplement to a revived welfare state.
In the footnote to this, they quote Alyssa Battistoni, “Alive in the Sunshine”, Jacobin 13, 2014 (p.4):
A UBI programme would ideally involve a transformation of the welfare state. Programmes that provide services must be kept and expanded – for example, healthcare, childcare, housing, public transport and internet access. All of these should be immediate goals of the left, not only for their inherent good but also because expanding public services is necessary for reducing overall energy consumption.
And in response to the question of why the rich should be given money as well as the poor, they respond (p.296):
As there would be no means-testing or other measures required to receive the UBI, it would break free of the disciplinary nature of welfare capitalism.
It is perfectly possible to disagree with any or all of this. That does however first require acknowledging it. And there’s a lot more where this came from…