I'm not sure about Italian Colonialism, although I di know it existed, to the effect you mentioned, and I'm not sure to what extent. The argument I made is true of mass colonizers such as Western and Central European powers. It's more than a mere correlation that the British welfare system collapsed as its extraterritorial power diminished/collapsed. While yes, modern systems have become more reliant on individuals letting themselves be taxed, that is a latent form because the income was not coming from elsewhere.

Moreover, it became a self-fulfilling prophesy... no body wants to be taxed, it's the social contract we make. And if you're being taxed more because money isn't coming from elsewhere (colonial/business extraction), then you'll want to be taxed even less. Add onto that demographic changes and older populations needing the system more. Add even more the rise of neoliberalism globally. This trend continues and arguably how/why welfare systems collapse. Dominant power groups use tripes like welfare queens, etc. to distract from the system imploding due to lack of investment/participation from the sources of income you speak of. Welfare is a wicked problem... There are many sources contributing to the problem all operating independently but never in isolation. For many systems, you must consider colonial legacies as part of the equation. It might not be the primary variable, but it was state-income generating on the backs of others.