No, that person is not correct on any of those points (I don't mean Xylene - I mean your "privacy expert").
You do not need permission to take photos in
most public places (there are
some areas that may restrict the use of cameras, such as amusement parks or concert venues) - and those pictured in the photos should have no expectation of privacy when in a public place.
One exception to the right to photograph people in a public place is that a photographer should not photograph something a person has a reasonable expectation of keeping private, even when this occurs in a public place - say a photograph of a woman whose skirt has blown up by the wind or a photograph of a person withdrawing money from an ATM machine.
Problems tend not to occur so much with the photo
taking as with the photo
publishing. In publishing a photo where people are recognizable
and where the photo is to be used in a
commercial manner, it is wise to get a release. When children are identifiable in a commercial-use photo, a release from the parents is necessary. Again, this would not be necessary for a photo taken of a crowd of people in a public place, even when children are present in the crowd.
People in public places give, essentially, what is known as "implied consent" to be photographed, as they have no expectation of privacy when they are in public. If someone were to come up to a photographer and object to his photo being taken, it is the smart photographer who backs off, but there is generally no legal necessity to do so.
Of course, the best way to avoid any lawsuit of any kind is to obtain releases from everyone photographed - but this is often impractical and basically unnecessary. Think of how difficult it would be, for instance, to obtain releases from everyone photographed in a football stadium.
As long as your photo is not used in a sensitive or controversial way (say to illustrate a story on a religious cult), you should have no problems with your intended use of the photos (except, perhaps, from this person who claims to be knowledgeable about privacy issues

).