Because Thomas Jefferson thought it would be only a matter of time before the American system of government degenerated into an “elective despotism,” he warned that citizens should act now in order to make sure that “the wolf [was kept] out of the fold.”
1785 seems rather early for Jefferson to be making such dire predictions about the unhappy fate of the new American government, yet his worry that democracy might turn into a form of despotism has proven to be correct if some 200 years later and “not a distant” time as he originally thought.
What is interesting about text below is also the use of animal imagery, this time seeing government as a “wolf” whose teeth and claws would need to be pulled if liberty were to survive.
All the powers of government, legislative, executive, and judiciary, result to the legislative body. The concentrating these in the same hands is precisely the definition of despotic government. It will be no alleviation that these powers will be exercised by a plurality of hands, and not by a single one. 173 despots would surely be as oppressive as one. Let those who doubt it turn their eyes on the republic of Venice. As little will it avail us that they are chosen by ourselves.
An elective despotism was not the government we fought for, but one which should not only be founded on free principles, but in which the powers of government should be so divided and balanced among several bodies of magistracy, as that no one could transcend their legal limits, without being effectually checked and restrained by the others.
For this reason that convention, which passed the ordinance of government  laid its foundation on this basis, that the legislative, executive and judiciary departments should be separate and distinct, so that no person should exercise the powers of more than one of them at the same time.
But no barrier was provided between these several powers. The judiciary and executive members were left dependent on the legislative, for their subsistence in office, and some of them for their continuance in it. If therefore the legislature assumes executive and judiciary powers, no opposition is likely to be made; nor, if made, can it be effectual; because in that case they may put their proceedings into the form of an act of assembly, which will render them obligatory on the other branches.
They have accordingly in many instances, decided rights which should have been left to judiciary controversy: and the direction of the executive, during the whole time of their session, is becoming habitual and familiar. And this is done with no ill intention. The views of the present members are perfectly upright. When they are led out of their regular province, it is by art in others, and inadvertence in themselves. And this will probably be the case for some  time to come. But it will not be a very long time.
Mankind soon learn to make interested uses of every right and power which they possess, or may assume. The public money and public liberty, intended to have been deposited with three branches of magistracy, but found inadvertently to be in the hands of one only, will soon be discovered to be sources of wealth and dominion to those who hold them; distinguished, too, by this tempting circumstance, that they are the instrument, as well as the object, of acquisition.
With money we will get men, said Cæsar, and with men we will get money. Nor should our assembly be deluded by the integrity of their own purposes, and conclude that these unlimited powers will never be abused, because themselves are not disposed to abuse them.
They [the assembly] should look forward to a time, and that not a distant one, when a corruption in this, as in the country from which we derive our origin, will have seized the heads of government, and be spread by them through the body of the people; when they will purchase the voices of the people, and make them pay the price. Human nature is the same on every side of the Atlantic, and will be alike influenced by the same causes.
The time to guard against corruption and tyranny, is before they shall have gotten hold of us. It is better to keep the wolf out of the fold, than to trust to drawing his teeth and talons after he shall have entered.