In his "Theodicy" (if I am not mistaken), Gottfried Leibniz famously claimed that this is the best of all possible worlds. Doesn't that imply that making the world a better place by inventing new technology is impossible? Did Leibniz respond to that? If so, how?
In Theodicy, Leibniz sets forth a universal argument. Appropriate to his Zeitgeist, the argument centres around the justification of God, however, it might well be read with a non-theological rearrangement, and actually, such a reading is what makes it relevant to the contemporary philosophy.
While particular manifestations of existence vary, they all are subservient to a unique universal rationality in all their aspects. Together they make up the actual world chosen out of the possible ones through "supreme reason" (Theodicy §8):
I call ‘World’ the whole succession and the whole agglomeration of all existent things, lest it be said that several worlds could have existed in different times and different places. For they must needs be reckoned all together as one world or, if you will, as one Universe. And even though one should fill all times and all places, it still remains true that one might have filled them in innumerable ways, and that there is an infinitude of possible worlds among which God must needs have chosen the best, since he does nothing without acting in accordance with supreme reason.
There is an overarching rational determinism binding whatever there are in that world (ibid., §288, emphasis in the original):
For it must be known that all things are connected in each one of the possible worlds: the universe, whatever it may be, is all of one piece, like an ocean: the least movement extends its effect there to any distance whatsoever, even though this effect become less perceptible in proportion to the distance. Therein God has ordered all things beforehand once for all, having foreseen prayers, good and bad actions, and all the rest; and each thing as an idea has contributed, before its existence, to the resolution that has been made upon the existence of all things; so that nothing can be changed in the universe (any more than in a number) save its essence or, if you will, save its numerical individuality.
The phrase “numerical individuality” signifies “individual and numerically one”. Hence, we have made out three key concepts of Leibniz's metaphysical view of the world: Rationality, determinism and individuality. As for individuality, we can deem Leibniz's view as a moderate streak of nominalism.
Leibniz seems to envisage the order of the world resembling the modern diagram of truth tree familiar to us from logic (caveat: I do not suggest this literally) such that there is a root which defines the rational order and the world actually emanating from the root (diagram borrowed from Logic Matters maintained by Peter Smith):
The development paths against rationality are not allowed, otherwise, the states of affairs take place as determined by the pre-established order.
Thus, the world changes —essentially, neither towards the worse, nor towards the better (that is, with respect to the questions of rational order, for instance, the problem of evil), simply according to the order, since it is already the best of the possible worlds. Then, the perennial question raises itself: What about the freedom of will? Leibniz thinks that the determinism he has depicted and the free will are compatible (see McKenna and Coates' SEoP article Compatibilism for a general discussion of the idea). He mentions three criteria: Spontaneity (in the sense of Aristotle's conception, i.e., absence of coercion), intelligence (the faculty to choose the good) and contingency (non-necessity). About them, he says:
I have proved that free will is the proximate cause of the evil of guilt, and consequently of the evil of punishment; although it is true that the original imperfection of creatures, which is already presented in the eternal ideas, is the first and most remote cause. M. Bayle nevertheless always disputes this use of the notion of free will; he will not have the cause of evil ascribed to it. One must listen to his objections, but first it will be well to throw further light on the nature of freedom. I have shown that freedom, according to the definition required in the schools of theology, consists in intelligence, which involves a clear knowledge of the object of deliberation, in spontaneity, whereby we determine, and in contingency, that is, in the exclusion of logical or metaphysical necessity. Intelligence is, as it were, the soul of freedom, and the rest is as its body and foundation. The free substance is self-determining and that according to the motive of good perceived by the understanding, which inclines it without compelling it: and all the conditions of freedom are comprised in these few words. It is nevertheless well to point out that the imperfection present in our knowledge and our spontaneity, and the infallible determination that is involved in our contingency, destroy neither freedom nor contingency.
From Leibniz's overall discussion, we understand that we have freedom of will that the determinism inclines us to enjoy rationally and we can follow our own course so far as we do not hit the bounds of rationality (viz., become contradictory).