1) Perhaps it is not clear to you, these people do not recognize the right of the Jewish people to their nation state within its own historic homeland, that is the state of Israel, and this is despite the fact that they are members of the Israeli parliament, the Knesset. This is one of the expression of democracty in this land of ours about which so many people abroad are critical. 2) These people broke the explicit law in at least two ways, and fortunately, we live in a state governed by democracy and the rull of law, unlike some countries you mentioned. 3) These people are not state officials representing the state of Israel. Indeed, they do exactly the opposite. Much of their purpose in taking this trip was to grab the attention of Arabs in Israel for purely political reasons, an aspect with which you may not be familiar, and in the process derived much delight at the anger expressed toward them by the public from left to right (check Haaretz, Ynet, & Maariv Hebrew sites).
from the article: Bar-On wants passports of Arab MKs who visited Syria revoked