Well, you would be erasing a flag if you leave it, once you are there.
There are lots of practical reasons to destroy a flag, the Boy Scouts cover the steps for destroying a flag. With all the issues facing this country, years of court debates about flag desecration (is anything with a flag on it sacred? do those cheap flags you buy for the lawn need to go in the trash or to a special facility) is so much misdirection from the real crisis. If you hear “flag desecration” is a campaign issue this fall, vote for the other guy, the one who is concerned about real problems.