In the time immediately after the Revolutionary War in the US, what was the attitude towards those who had supported Britain?

British troops and allies evacuate New York in November 1783.
The narrative for this topic usually begins and ends with the fact that more than 60,000 Loyalists fled the country when British troops left after the Treaty of Paris. Many went to Canada, where they formed a segment of the population uniquely loyal to the British Empire. But that isn’t the whole story. A more comprehensive answer is much more complex, and ends up with the fact that most Loyalists were able to rejoin American society after the war. As one historian puts it:
“After the American Revolution a number of Loyalists, those colonial Americans who remained loyal to England during the War for Independence, did not relocate to the other dominions of the British Empire. Instead, they sought to return to their homes and restart their lives. Despite fierce opposition to their return from all across the Confederation, their attempts to become part of a newly independent America were generally successful. Thus, after several years of struggle most former Loyalists who wanted to return were able to do so.” (Aaron Coleman, PhD, currently professor of history at the University of the Cumberlands in Kentucky.)
The War of Independence was long and hard. Loyalist militias and volunteer units had fought with the British, burning homes of Patriots and fighting battles against Continental forces. Obviously many people in the new country had serious grievances against Loyalists.
During the war, the situation for Loyalists was quite variable. The loyalist position became untenable in large parts of the Thirteen Colonies quite quickly after independence was declared and the patriot faction seized control of most of the country. People might maintain loyalist sympathy but could do little about it in many areas. It was dangerous to be a loyalist in Massachusetts or Rhode Island, for example.
Loyalists had more latitude in contested areas like New Jersey and parts of the Carolinas, and in areas actually occupied by the British, such as New York City and Charleston, South Carolina. New York outside of the city was also rife with Loyalists, by all accounts.
All the rebellious provinces passed laws to penalize loyalists, or people who refused to take an oath of loyalty to the new government. In most cases, the property of Crown loyalists could be seized and used for the benefit of Patriots, although this was not always done.
Retribution fell especially on Loyalists who continued to serve the crown or the British forces, and on those who actively served in loyal militias or as fulltime soldiers in pro-British units, the “Provincial Corps.” Some historians estimate that up to 20,000 Americans served in the “Provincial” units, not to mention those who served in part-time militias. (Others serving in the Provincials included residents of Nova Scotia and Scots who were in the process of emigrating to America.)
In some cases, Patriots took great exception to the participation of Loyalists in British units. Several Loyalist officers were captured in the Patriot victory at Kings Mountain. The next day, eight or nine of them were tried and hanged, supposedly in retribution for similar treatment meted out to side-switching Patriots by the British. Bloody business all around.
Some of the more active Loyalists fled with the British forces when they evacuated New York and Charleston, after the Treaty of Paris. It is estimated that at least 60,000 Loyalists left the country, and perhaps as many as 100,000, especially when enslaved people held by Loyalists are included in the estimate. A number of former slaves who had served with the British, and were given their freedom as a result, also left with the British, many of them to Canada.
Canada was the refuge for maybe half of the Loyalists who left with the peace. Others went to nearby Florida (still British territory), the islands of the Caribbean, and other destinations.
However, consider that at least a fifth of the white population of the Thirteen Colonies was loyal to the crown to some extent. That’s maybe half a million Loyalists, of whom 100,000, tops, left the country. So clearly, many thousands of Loyalists remained in their homes and simply made the best of it in the new country, reintegrating as they could and as wartime passions cooled.
Some became prominent citizens, such as Richard Harison, a lawyer in New York who worked his way back into the good graces of the establishment and was appointed by President Washington as Federal District Attorney for the state.
So, it isn’t true that they all fled the country or suffered reprisals. The war was over, the last vestiges of British rule ended, and people got on with their lives.
See: Paul H. Smith (1968). The American Loyalists: Notes on Their Organization and Numerical Strength. The William and Mary Quarterly, 25(2), 259. doi:10.2307/1919095
Aaron N. Coleman (2008).Loyalists in war, American in peace: The reintegration of the Loyalists, 1775-1800. PhD dissertation at University of Kentucky. LOYALISTS IN WAR, AMERICANS IN PEACE: THE REINTEGRATION OF THE LOYALISTS, 1775-1800
Daniel J. Hulsebosch (2016). Exile, Choice, and Loyalism: Taking and Restoring Dignity in the American Revolution. Law & Social Inquiry, 41(4), 841–865. (ABA, 2016) doi:10.1111/lsi.12215