While it is true that there was a previous Fugitive Slave Act of 1793, it has to be recognized that the Fugitive Slave Act of 1850 was a much more stringent beast, which really did make for significant penalties for those involved in aiding and abetting those slaves who escaped their enslavement to the free Northern States.
The legislation so passed was part of the general compromise of 1850, in which those in the political field had to do what they felt needed to be done to keep the sectional conflicts between the North and the South from getting worse, and therefore needed to reach a compromise that would effectively keep the dogs at bay. Regrettably, this meant that those who were enslaved found their situation to be even more intolerable than it was before, because the Fugitive Slave Act of 1850 mandated that citizens were compelled to assist in the recovery of slaves who had escaped to the North, in addition to the fact that jury trials were now eradicated, as well as harsh penalties were now imposed on those taking part in aiding the escape of slaves, and finally the Federal judges assigned to cases of escape slaves were paid twice as much when they ruled in favor of the slaveholder.
All of this pretty much meant that the North was no longer the true refuge of those escaping from slavery, because the impact of this legislation was the hand of this law extended into all the States of the Union, of which, the penalties for those that felt it to be their ethical obligation to do their fair part to dismantle slavery, were subject to that law being turned against them.
That said, as much as the South was well pleased with the passage of this Act, the bottom line is that in all practicality, it served to make the division between those of the North as contrasted to those of the South, even more stark, which exacerbated the whole slavery issue, because it made the slavery issue to be of even more concern to those of the North, because slavery was not only inimical to what the Declaration of Independence contended, but also it clearly indicated that slavery as an issue was not going to go away, which stuck in the craw of those liberal and fair minded people that saw the enslavement of a fellow man as unacceptable and anathema to a liberty loving people.
So too, the North had eradicated slavery in all of its States by 1850, which signified that they did not countenance slavery, and the fact that they would no longer be considered to be a sanctuary for those desiring freedom from the oppressive state that they were in, was not something that they wished to see imposed upon them, which meant that slavery could not simply be out of sight and thus out of mind, because the South made it to be its point, that it would always be in the whole nation’s sight, and because of that, the cold winds of the Civil War had been sowed, and the reaping of the fierce whirlwind of that war would soon come.