Having been smitten by philosophy (after discovering Thomism) even within the past year, it is now time for a backlash.
After all, if I really believed in the necessity of philosophy I would be Roman Catholic rather than (sort of) Orthodox...
Here is Charles Murray's list of the most important philosophers from his book Human Accomplishment - in order of importance:
Philosopher Index score
John Locke 37
The question is - which of these philosophers have done good, which have done harm, and which made no difference either way?
My own feeling is that almost all of them did net harm or made no difference outside of profesional philosophy - exceptions being (probably) Plato, Aristotle and Augustine.
Aquinas's was a remarkable achievement - the most comprehensive system - and he was a very good man; but Scholasticism is overall 'a bad thing' since it leads Christianity to put philosophy at its root, and thereby brings Christian philosophy under the sway of fads and fashions in academia.
(A survey of Roman Catholic philosophy - like Alasdair MacIntyre's God, Philosophy, Universities - shows that the RC church has for 1000 years been ravaged by philosophical disputations which went back and forth and led nowhere).
Kant, Descartes, Hegel, John Locke, Hume, Spinoza, Schopenhauer, Berkeley, Nietzsche, Hobbes, Russell and Rousseau seem pretty obviously to have been pernicious influences. Although some wrote excellent prose; overall, from the perspective of human life as a whole, it would have been better if they had not been.
Plotinus and Fichte were harmless because barely significant and technical.
Socrates - I'm not sure. He might have been a very good thing, or a very bad thing - and where the balance comes out... Well, I keep changing my mind.