On an episode of Sleepy Hollow, Det. Mills asks time-traveling Revolutionary War soldier Ichabod what the heck the Fathers were thinking with the Second Amendment, and he says that several of his compatriots had misgivings about it. Was there any actual historical pushback on the Second Amendment?

There was a fair amount of discussion about the 2nd amendment but it really doesn't matter in a historical context. You can see this for the total scope of the conversation, however to understand the 2nd amendment properly you need to understand the Supreme Court.

Starting with Marbury v. Madison the role of the court started to take shape and the concept known as "judicial activism" began making an appearance more and more in the beginning of the 20th century.

A very important concept in American law is known as nulla poene sine lege which means that something cannot be punishable unless it is specifically illegal. In US v. Cruikshank the court found that the right to own a firearm is not derived from the 2nd amendment, or the constitution, which sounds like you don't have the right to own a gun, however in US v. Heller the court affirmed that you do in fact have a personal right to own a gun on the basis that the constitution does not restrict it and therefore it must be legal to do.

The 2nd amendment itself, according to the court in Heller, was a widely accepted right that has roots in the English Bill of Rights in 1689:

This meaning is strongly confirmed by the historical background of the Second Amendment. We look to this because it has always been widely understood that the Second Amendment, like the First and Fourth Amendments, codified a pre-existing right. The very text of the Second Amendment implicitly recognizes the pre-existence of the right and declares only that it “shall not be infringed.” As we (the United States Supreme Court) said in United States v. Cruikshank, 92 U. S. 542, 553 (1876), “[t]his is not a right granted by the Constitution. Neither is it in any manner dependent upon that instrument for its existence. The Second amendment declares that it shall not be infringed ..”. Between the Restoration and the Glorious Revolution, the Stuart Kings Charles II and James II succeeded in using select militias loyal to them to suppress political dissidents, in part by disarming their opponents. See J. Malcolm, To Keep and Bear Arms 31–53 (1994) (hereinafter Malcolm); L. Schwoerer, The Declaration of Rights, 1689, p. 76 (1981). Under the auspices of the 1671 Game Act, for example, the Catholic James II had ordered general disarmaments of regions home to his Protestant enemies. See Malcolm 103–106. These experiences caused Englishmen to be extremely wary of concentrated military forces run by the state and to be jealous of their arms. They accordingly obtained an assurance from William and Mary, in the Declaration of Right (which was codified as the English Bill of Rights), that Protestants would never be disarmed: “That the subjects which are Protestants may have arms for their defense suitable to their conditions and as allowed by law.” 1 W. & M., c. 2, §7, in 3 Eng. Stat. at Large 441 (1689). This right has long been understood to be the predecessor to our Second Amendment. See E. Dumbauld, The Bill of Rights and What It Means Today 51 (1957); W. Rawle, A View of the Constitution of the United States of America 122 (1825) (hereinafter Rawle).

So you see... even if the 2nd amendment didn't exist, we would likely still have the right to own a firearm assuming that all things stayed equal in terms of how SCOTUS evolved since Marbury. In fact, the 2nd amendment itself only refers to Congress and has nothing to do with your personal right to own a firearm.