There is some logic in your post. However, for justice to be served (in the absense of justice for the Palestinians in Israel), there has to be some consensus from external parties to decide on what would be just. In this case it would be the United Nations. The UN has (IMO rightfully) ruled against Israel in virtually every instance of "ownership" of the land.
Of course the Likudniks would have you believe that the UN discriminates unfairly against Israel. This "spin" is so widespread that many Israeli supporters actually believe it.
Even in Canada, the First Nations have the laws available to them to pursue land claims (and I am aware that the pace of justice here is slow), and Canadians accept the decision of the courts. The fact that it may be many generations later is not relevant when it comes to the law. Palestinians have no such right in Israel and the theoretical right even in the occupied territories has shown to be a sham.
Bottom line....somebody has to administer justice and there is no better tool than the UN at the moment.
The absence of better tools for "ruling" on the Israeli/Palestinian conflict doesn't mean that the UN is impartial or will rule fairly for all involved. Things like the number of member/nation states (the bulk of the Arab nations) opposed or openly hostile to Israel cast doubt as to whether the UN would ever pass anything akin to a "fair" judgement on the matter and who is going to willingly submit to such a judgement if they doubt process in which it is derived? There has to be a dispute mechanism that all parties have faith in, for it to work, and the UN has repeatedly shown itself to be too susceptible to the nationalist (and populist) goals/agendas of its members. For all the good intentions of some members, I wouldn't want/trust the UN administering what it calls "justice" on my country either.
I'm not pro one side or the other in the Palestinian conflict: I see a lot of blame and reasons for distrust on both sides and until someone emerges, be they an individual, organization or nation that both sides are willing to trust, this will continue as it has been.
Back to Galloway, I still fail to see how banning a foreign national from entering the country when he may have violated our laws regarding supporting terrorism is a violation of freedom of speech, especially when there are no restrictions on broadcasting or publishing his views (and whatever else people want to say about the gov't they have been emphatic on that point). Trying to draw comparisons to Jason Kenney or members of the Liberals attending rallies of "questionable" doesn't work for both the reasons of citizenship and the degree of involvement: its not a crime in this country to listen to a "terrorist" organization, or anyone else's views, its just a crime to give them material support.