You make some good points, and I'm very surprised your post hasn't been modded down.
In my opinion this migration will be a massive drain on the EU and especially on the countries that support the immigrants. Perhaps countries like Germany and Sweden can afford to house, feed and support these(almost) millions, all while maintaining their current expenditures for citizens and pensioners already there. Time will tell.
However, I can imagine one thing is for sure, the internal security services tasked with maintaining watch over "islamic terrorists", etc; are going to be over burdened with all the new "persons of interest". They already know there are many who have piggy backed onto the mainly Syrian population trying to get into Europe. It really is quite a mess.
Yes, I would imagine the vast majority of immigrants didn't want to leave their homeland and only want a normal life for their families. But at the same time, it would be quite naive to not acknowledge, especially in light of where the migrants originated, that there wouldn't be those whose goal is to cause harm to "The West" or "The Great Satan".
The really interesting thing watching this debacle unfold is how the EU is straining to keep their solidarity in line. Hungary, Serbia, Croatia, Greece, Austria, etc; have all gone about managing this differently, which is really to be expected. Europe had no gameplan in place for something of this magnitude and is really unprecedented.
Also, a bit of disclosure, I live in the US, in a neighborhood with a very high percentage of immigrants, from all over the world. I am around lots of people from Africa, Asia, the Middle East and Latin America on a daily basis, because I use Public Transit a lot. I actually enjoy the sort of cosmopolitan environment. The US is actually setup fairly well to absorb immigrants from refugee status countries, as opposed to economic refugees(yes, this is a sensitive topic I know).