If we simplify people for the sake of argument we can create two groups of people. Those willing to change. Those unwilling to change.
In reality everyone is willing to change some things and unwilling to change other things. Exactly what can be changed varies with the person and the culture that the person is involved in.
Does muching at Mickey D's make people "American"? Of course not. If a French person buys a burger that person is still French. However, food is something the French have identified their culture with so many people in France think the food at Mickey D's disgraces their culture. Sure, it really sucks and we all know that, but, the United States does not identify their culture with Mickey D's. We identify our culture with patriotism, freedom, democracy, achievement, high standards of living. Mickey D's represents achievement in business rather than a high quality of food. Mickey D's represents the speed at which "Americans" progress.
But people in France don't associate Mickey D's with speed of progress or achievement in business. Many people associate Mickey D's with crappy food. Why would anyone want to embrace this garbage?
But cultural change is unavoidable. Sure, we can make Mickey D's illegal and the next thing you know we have the "War on Burgers" which would be a lot like the "War on Drugs" with hidden butcher shops like we have hidden drug labs.
When cultures come into contact we exchange values, customs, traditions and resources. Eventually the cultures coming into contact change to the point where they are no longer what they were. Typically the predominate culture will absorb the sub culture.
So what happens when two predominate cultures clash? They either destroy each other, absorb each other or one ends up dominating the other.
Take the current clash between Islamic cultures and Western cultures. I can guarantee that one of these two cultures will predominate the other. The two cultures have too many mutually exclusive customs and traditions. Both cultures are dependent on each other in the exchange of resources and as long as the contact exists the conflict will exist.
Which one will predominate the other? If I have to guess I would say that the Islamic nations were going to eventually dominate Western cultures and eventually Eastern cultures. That is just an opinion based on my assessment of perseverance and democracy. The Islamic nations are willing to kill off all opposition culture and the Western nations are not. The last culture left standing is predominate so ....
Even if each culture closed itself off from the other the economic pressures of co-existence would eventually force them into conflict.
We can't stop cultural change. We can attempt to manage it. The founding fathers of the United States attempted to build a constitution which incorporated the ability to plan for cultural change while ensuring specific rights. Today people are trying to eliminate some of those civil rights, like the right to keep and bare arms :-).
Democracies can change their protected rights, the right to freedom of speech is not the same in the United States and the United Kingdom. In both places it can be changed to prevent "hate speech" like speaking out against the religion of Islam.
However Islamic Law cannot change to allow speaking out against the religion of Islam.
One culture can change and exist. The other cannot change and exist.
But cultural change can't be avoided? Right and the incorporation of the West and East into Islam will result in some changes. Islam has changed some in the last 1500 years and will change some more, however, there are some things that cannot and will not change because they are fundamental to the culture.
The Catholic church might allow priests to marry again, but, they will not eliminate the Pope. The Christian church may dress in black or white or red or rainbows but they won't eliminate the Cross. People may interpret the Bible differently but they won't eliminate the Bible.
Western cultures won't eliminate democracy or constitutions but those constitutions can change because democracies can vote to change them.
When two cultures clash they will change and eventually stabilize into some new form. What can be changed will change and what cannot change will not change. If the predominate culture is unwilling to accept the existence of those things that will not change the things that cannot change will be eliminated or be hidden from the predominate culture.
Religion in the U.S.S.R. Drugs in the United States. Prostitution almost everywhere. These things go into hiding because some people want them and other people are unwilling to accept their existence.
There are two prerequisites for elimination or being forced into the "underground". The first is the unwillingness of the predominate culture to accept the existence of whatever custom, value or tradition is unacceptable. The second is the unwillingness of those who participate in the unacceptable value, custom or tradition to cease participation.