Another Canadian perspective here.
My preference would be for retail outlets not to be open on statutory holidays such as Thanksgiving. Mainly because it seems to add to the 'specialness' of the day when the immediate world shuts down and one has the opportunity to close in upon oneself and re-group, either with or without family.
However, what came first? The chicken or the egg? Are the stores opening to create consumer demand, or did consumer demand cause the stores to open?
I remember when Sunday shopping was becoming an issue. Limited opening was starting to be permitted, but only in designated tourist areas. But even before that, retailers. both large and small, were beginning to flout the law and open their doors. They would then be fined sometimes thousands of dollars, which they would pay and then open right up the following Sunday. The profits they were making well exceeded the fines, and it almost became just another cost of doing business. This still happens on stat holidays, where if you are not in a designated area, you cannot legally open. Some retailers still do, and still incur the fines.
If I remember correctly, somebody upthread put forth the thought that if July 4th (your Independence Day) was in a different season, then lifeguards would not be considered essential workers and could have the day off. But if July 4th was actually February 4th, then would that not make ski-lift operators, or more accurately rescue teams, become the essential staff?
I do agree completely that the exploitation of part-time workers forced to work without additional compensation is morally and should be legally unsupportable. Here, the laws vary province to province, but on the whole they are pretty stringent on making sure that workers get premium pay or time in lieu for working on a Stat.