They are right in their observation as to the effect. The issue is that carrying a long gun isn't convenient like carrying a holstered handgun while conducting day to day business. Depending on the manner of carry it also incurs the appearance of holding the firearm in a user's grip as I have seen in some pictures - when carrying a handgun in a holster you NEVER are doing this at any time other than at a range, gun store or other place where handling of firearms is part of the business.
Now, if there was a riot in progresss I would say that open carry of a long gun is a very good idea as it allows one or several people to turn back a violent mob (hoepfully without having to fire). Open carrying a hunting arm etc in a place that is by an area one is hunting would also be a more routine thing.
Having one out in suburbia and taking it with you whlie shopping... Thats a lot of weight to carry along with the items you are purchasing.