I do not think that violent clashes between cultures are inevitable, nor even normal. Rather, I think that the differences between cultures are exploited by people seeking to parlay the fears and uncertainties of people into political gain and personal advantage.
The things we are concerned about - the enforced adherence to a religion or world view, the violent opposition to other views - are in my view possible only in societies of the uneducated and indigent. So my view is that the range of social positions I advocate - from anti-poverty measures to education to openness - act inherently against these sorts of cultural conflicts.
Why is education important in this context? I liked what you sent by email: "education is simply society's expression of the meaningful life." People who take up nationalism or religion or any of a hundred various causes are looking for meaning in their lives, and this desire is strong enough that it is easily manipulated. Education provides a counterweight to this: a person who already has some sense of meaning is much less likely to be drawn into violent or oppressive factions.
There is always a temptation on the part of those who defend society to ensure through some legislation or fiat that people's lives are directed appropriately - just as there has always been the temptation on the part of those who defend democracy to ensure that people's votes are directed appropriately. When the people of Chile elected a communist, when the people of Algeria elected fundamentalists, when the people of Palestine elected Hamas - we look at these events and say 'democracy failed', and seek to move with force against them. And just so, we seek to move against those who would abuse their freedom of speech, using it to hurt instead of to enlighten.
But to respond by overthrowing democracy, or blocking freedom of speech, is exactly the wrong response. It is never possible to teach people how to make correct choices by taking away their right to choose. People will elect good governments, and utter good statements, when they have learned how: when they have learned what sort of governments not to elect, what sort of things not to say. And, sometimes, this can be learned only by doing the wrong thing.
My own view is that we need to teach ourselves how to use democracy, how to use freedom, and that this process takes place one person at a time, through a long and difficult process, rather than through the point of a gun. And we teach people through the use of example, by modelling and demonstrating the attitudes and actions of a person who is genuinely free and genuinely committed to democracy.
This is what Gandhi understood. People often oppose non-violence because there are cases where it does not work. But Gandhi would never deny that. What Gandhi tried to do was to model and demonstrate how political leadership is appropriately conducted, an act of civilization that eventually shamed the British into acquiescence.
True, some people will never be shamed, and thus it is true that in some cases the injustices will continue. But everyone can learn, and the act of modelling and demonstration will, inevitably, teach. And the change will ultimately be made where it is most needed - no, not in the government, but in the people.