There is no right to roam the countryside on other peoples private property. Some one has purchased that land and you have no right to roam on it without their permission. Would you like it if someone else just went into your backyard and roamed around, no, and neither do they.
I feel that private property must be respected. In areas that I live such as Kansas a lot of land is dedicated to the growth of crops. If those crops are trampled on or disease is spread to them you are taking away another persons income and food. I feel a person has a right to keep there property private and that anyone who does not respect that right should be reported to the local authorities.