In the current discussion about immigration there has a lot of debate of what is appropriate or inappropriate for a immigrant to do. Is it appropriate for a refugee to visit the allegedly dangerous country of origin? Should we consider all things that are appropriate for locals to be appropriate for an immigrant, and all things that are inappropriate for locals to be inappropriate for immigrants, etc., etc.
These are all interesting and useful things to discuss, but I don't think that this is really the point. I think that the main point of the immigration and multiculturalism discussion should be the fact that large populations of immigrants make changes to the culture, both desirable and undesirable, and there are a lot of things that are quite OK in individual immigrants, but that are undesirable in large groups, and that if the country is considering admitting a large group of immigrants the country should also consider the changes that that group is likely to bring, and then decide whether the group is desirable or not, and if yes, what should be done to fix the negatives.
Take me, for example. People don't usually want to throw me out of the country, and there is no reason they should. I am a fairly harmless immigrant: more or less law-abiding (might drink wine in the park in violation of the city ordinance or even watch DVDs on a Linux computer in violation of Lex Karpela, but I don't kill, rob, rape, shoplift, drive drunk, or leave trash on the grass after drinking that wine in that park). I also have a lot of personal traits that are nothing to be proud of, but then so do many Finns, so this is beside the point. But I am also a product of another culture (three cultures, actually), and if you suddenly decide to admit ten thousand of me, you really should consider the consequences.
I won't go into all the details of the cultural differences, but here are several examples: I don't give a shit about environment, I want stores to be open round the clock, and I like drinks made of ice coffee and ice cream in a blender. The first one is the sort of thing that most Finns would consider negative; the second will find both support and opposition among the Finns, and the third one is the kind that nobody probably minds much.
There is nothing illegal about a person not giving a shit about the environment (as long as they don't commit environmental crimes), or indeed about a person who would like to live under Sharia (as long as the person doesn't do anything illegal about it). Accepting a lot of such people, however, will reduce the average concern for environment, or increase the average push for Sharia, and this should be discussed, preferably before rather than after. Because, among other things, after you admit immigrants you really can't tell them that they are not allowed to hold some views or advocate some (legal) things.
None of these is really relevant for individual immigration. If a New Zealander comes here to work, or a Nepalese marries a Finn and moves here, or a Brazilian comes here to study, or a Jewish-Russian-American comes here to study and then stays to work, their power to affect society is rather minimal because there are so few of them, so as long as they are not committing crimes there is no reason anyone should care. But any time you decide to admit a large group, whether they are Somali refugees, Russians with Finnish ancestry, or large groups of guest workers from wherever, the cultural impact should be discussed.
If you accept a lot of people like me, you will notice that the concern for environment will go down, the pressure to allow stores to be open whenever they want will go up, and lots of coffee and ice cream drinks will appear in coffee places. You might well consider it acceptable damage. You might teach people like me to go through some environmental motions just to please people like you (and, in my case, some of you have). Those of you who want stores to be open whenever they want, and/or like drinks made of coffee and ice cream might consider us a positive impact and say that we actually enrich your culture. But you should think about it, and discuss it among yourselves, before you let us in. Meaning: really think about it. Not just assume that we are exactly like you. Not assume that we will enrich your culture. Not assume that we will all be on welfare and rape all your men. But actually try to figure out what we are, what the impact will be, and whether the positives outweigh the negatives.