July 4th is strictly a secular/nationalist holiday. It commemorates a political act – signing the Declaration of Independence from merry olde England, making possible the United States as we know it today, where we can show ourselves as frum Jews with pride and without fear.
When you look at it that way, observing July 4th in at least some way is a matter of Hakaras Hatov. If you don’t like barbecues, fly the American flag.