I mean, it totally can be a smaller state and do that. The spending that these people want more of are things like law enforcement and defence - which are big budgets in £ terms, but do not account for particularly large %s of public spending relative to things like health and social care, education, pensions and benefits, etc.
These people believe they can shrink the state dramatically whilst still spending a lot more on their pet issues. When you look at the size of the various budgets, they're not wrong factually. So I'd focus your fire on the ways in which they're wrong morally and philosophically.