If you insist they give up their culture immediately you will be seen as trying to take away their culture. Just like how gun rights advocates perceive attacks on gun culture.
Solidarity is a normal reaction to real or perceived hostility. In history the social pressure to assimilate resulted in immigrant collectivism in order to support each other; Chinatowns, little Italy and a myriad other ethnic enclaves formed partly because of this pressure.
I provided those links as evidence that your claim of "unrestricted immigration" was false. And you have not provided any evidence in support.
Again, you have not provided evidence. That is a narrative which extrapolates from news reports which are not representative of everyday life. There are reports from citizens that run contrary to the fearmongering in the media, that say that nothing much is happening.
Unfortunately people are allowed to campaign for legal changes that you don't like. Like Christians who run gay conversion camps and campaign to restrict gay rights. Or make abortions illegal. Or ban certain types of headgear. It is your responsibility to demonstrate the benefits of your preferred legal setup.
You paint Muslims with one brush based on media reports and ignore the countless examples that don't fit the stereotype you cling to. There are already millions of Muslims in your country and all you can point to are a handful of radical preachers and a handful of terror attacks over a decade or more. Every day there are millions of peaceful secular interactions with Muslims and Christians.
You started this conversation objecting to unrestricted immigration (only tangentially related to my post on how assimilation takes time) and when I challenged that, you changed the subject. Now you want to discuss (again without real evidence, only media reports) the state of Europe and broad prejudicial stereotypes about Muslims.
For example, the Christian faith also tells them not to conform to the world around them and you give them a pass. And they campaign against things that impact your life and society: abortion, gay rights, trans rights, secular government, "indecent" works and secular education. Not to mention the Jehovah's Witnesses literally trying to convert people.
You can't reason someone out of a belief they weren't reasoned into.