How is it not the wrong message? You're encouraging people to immigrate at great peril and then saying multiculturalism doesn't work which means to me whatever dream you're being sold will never become a reality. Assimilation is a two way street.
The tone of your comment kinda gave it away.
They immigrated to escape danger, and Germany accepted them, they had no responsibility to even do that, let alone change their values to accomodate them.
Was it the humane thing to do? Yes. Did Merkel speak out in support of letting them in? Yes, and that's admirable, but that doesn't mean they have to go to the extreme of completely altering their way of life to now adapt to those refugees. She didn't say come here and pursue a whole new life where you'll have complete freedom to be who you are (she didn't sell them a dream). She basically said we have an obligation as good human beings to help these people escape danger, they've already done that, and at the time 49% of Germans disapproved, only 39% approved of it. She's gone above and beyond in that sense to help these people, she compromised her popularity among her own citizens to help them.
And she also didn't say by reducing the immigrants that she means send them back to where they came from. If she pushes for that in the midst of the same crisis they fled to escape then that's terrible statesmanship, and just ethically wrong, but if she is just asking for help from other countries in the world, like she has done already, or using extreme political rhetoric to make the refugees assimilate faster, there's nothing wrong with that.
If the refugees can and want to adapt to Germany's way of life, and in the years and decades to come end up making up a large portion of the population then Germany's culture should naturally assimilate to their views and beliefs, but in the mean time Germany, or any country for that matter, has no responsibility to immediately and forcefully alter their values for incoming immigrants.