Spending is great if it's spent on a true investment. Building Hoover Dam is an example of huge government sized spending that has an actual return on investment. In most cases though government spending is the most wasteful kind of spending there is and has a negative return on investment. I don't think Keynes ever argued for destroying wealth. His ideas were hijacked by the left to justify envy driven confiscation and destruction of other people's money.
That said, I always thought that Keynes believed in a kind of bottom up econ model, where if people were put to work (even on borrowed money) they would stimulate a demand for goods and services that would put others to work. (Sounds so nice, doesn't it?) The lefties' welfare philosophy follows the same model. I have heard liberals say that each person on welfare creates another job (some even say more).
Corrections invited (or I could even look it up).