Well if people in those countries want to be Muslim, what does it matter? As long as they keep laws in place for the democratic majority of the country the religion of individuals shouldn't matter.
It just doesn't happen that way. In certain areas of France it's generally understood that 90% of the crime is from the immigrant populations. Muslims will insist on having Muslims for their elected representatives if they can vote. The local governments will become Muslim. Then the larger regional governments will begin to change too. They form their own small communities where their customs are enforced. What you say just doesn't happen. They put their religion and customs above the law to the extent that they are able to.
I understand how Muslims move into a country and, due to the politics of the Islamic faith, consolidate and try to "usurp" the local government. I was trying to get at the point that the problem is the immigration and not the religion. If the religion starts to propagate then that's what it does, all faiths try to do this.