[Ken H]

To walk all over the U.S. flag is illegal.

Not if the person owns the flag. It's their private property.

[Enlightened1]

Wrong....

“Whoever knowingly mutilates, defaces,
physically defiles, burns, maintains on the floor
or ground, or tramples upon any flag of the
United States shall be fined under this title or
imprisoned for not more than one year, or both.”

http://www.gpo.gov/fdsys/pkg/USCODE-2012-title18/pdf/USCODE-2012-title18-partI-chap33-sec700.pdf