How so? The Patriot was based on the Swamp Fox, who was a real person. The argument over going to was in SC. was real. There were a lot of Colonists who didn't want to go to war. I'm from SC. I know, I am a History major and one of my Professors cited that movie as bieng very accurate. The way the British soldiers acted towards Colonists(Corwallace) was accurate. The British at that point were sick of the Colonist, they hated them. The Battle at Cowpens really went down that way. The beach that the "Rebels" hid at was the Swamp Fox's real hide out. I don't see your argument. Another movie I would suggest is "Glory"
Like Pearl Harbor did with Ben Affleck's character, who amazingly flew in the Eagle Squadrons, shot down several Japanese planes at Pearl Harbor,
and flew in the Doolittle Raid (all based on real people and events, but not with the same person involved in all three); instead of focusing on the exploits of one real historical figure, they made Gibson's Ben Martin a composite of several people in order to create an Übercharacter who is able to depict multiple aspects of the war and exhibit or omit the qualities of the character that they don't feel aid the story. Which is fine from a storytelling standpoint and makes things more entertaining than reality, but in turn shouldn't be held up for its historical accuracy.
You mention Francis Marion "The Swamp Fox," for instance. He was indeed one of the sources for the Ben Martin composite character (along with Daniel Morgan, Andrew Pickens, Thomas Sumter, and others). He was also a slave owner, yet they glossed over that fact in favor of the kid glove treatment of having all the black farmhands and servants be what were called Free Negroes living harmoniously with Marten, because I guess they felt the audience couldn't handle the realistic duality of a man fighting for freedom while owning slaves and comment on the inherent hypocrisy of that. It was a whitewashing of history that was the biggest criticism of the film. Since they were fine with acknowledging his brutality against the Cherokee, I don't know why they shied away from this aspect of his history.
It was Andrew Pickens' South Carolina militia who fought at the Battle of Cowpens, not Marion. In fact, the Battle of Cowpens in the film was itself a composite of Cowpens and the subsequent Battle of Guilford Courthouse. Col. Tarleton led the British detachment at Cowpens that was soundly defeated due to the trap presented by the "retreating" militia, and Cornwallis was not present. It was at Guilford Courthouse that Cornwallis ordered the bayonet charge and the firing of grapeshot into the mass of troops which killed many of his own men along with the Colonials, while indeed breaking their lines. Guildford Courthouse was technically a loss for the Colonials but it was a Pyrrhic victory for Cornwallis which prompted him to halt his pursuit of Nathanael Greene and instead retire to Wilmington, North Carolina and eventually Virginia, which led to him eventually being cut-off and to the surrender at Yorktown.
Speaking of Banastre Tarleton (Tavington in the film), while he indeed had a reputation for his brutality against the enemy, that reputation was not entirely fair. In the Waxhaw Massacre that earned him that reputation for instance (and was a rallying cry for the Southern Colonials similar to The Alamo decades later), he allowed the Colonials under Buford to surrender, but his horse was shot out from under him, which made his Loyalist troops think he had been killed and prompted them to charge and brutally massacre many of the surrendering Colonials with their bayonets and sabers. Tarleton himself wrote about the carnage and vindictiveness of the attack, and clearly considered it shameful even though he had not ordered the charge. There's certainly no indication that he (or anyone else in the Revolution) ever locked an entire town in their church and burned them alive, set fire to dozens of farms solely to punish his enemy (though they often did burn farms for other reasons), or shot non-combatant children and slaves who wouldn't give up information on their owners. He also was not as nearly as old as his character (he was only 26 at the time of the film) not poverty stricken but from a wealthy slave-trading family, not a disgrace to his superiors, not unable to return home and forced to stay in the Americas, and not killed at Cowpens. In fact he returned to Britain a hero, was eventually promoted to full General, and became a baronet and member of Parliament before dying - long after Marion - in 1833.
While the Southern campaign and the Revolution in general was a lot more brutal than is commonly depicted and atrocities were committed on both sides, the savage acts against civilians in the movie seemed more like Emerich playing upon the actions of the SS from his native Germany than anything typical of the British during the Revolution. The film should be commended for including the brutality amongst the two warring enemies, but it took it too far in the other direction in the process and slandered real people like Tarleton and Cornwallis, who was depicted as approving of the brutality against civilians when he became desperate to catch Martin.
I'll give you that the film was aiming to capture the spirit of the Southern theater of war and some of the personalities in it, but to call it largely historically truthful is inaccurate (the same applies to almost all Hollywood historical films). I hope your professor mentioned some of these differences when he recommended the film. It was the composite fictionalized nature of the characters and events which allows for both whitewashing of certain less desirable aspects of the protagonists while playing up the brutality of the antagonists that prompted me to compare it to 'Pearl Harbor,' where similar composite characters were also used. 'The Patriot' is certainly better than 'Pearl Harbor' though, and was an entertaining movie regardless.