Who’s Laffing Now?

As the economist Arthur Laffer pointed out in the 1970s, increasing the rates levied by certain taxes will actually reduce overall revenue.
The UK Budget will be announced later today, and there is talk of some tax rates going up, especially taxes on capital.
And that’s where I’m confused, because critics of any increase in such rates predict diminishing returns. Surely a reduction in overall taxation is a good thing?
Or could it be that so many entrepreneurs would simply emigrate, leaving us all much worse off?