The assessment isn't based on real experience and is instead informed by four decades of tabloid scare-mongering, thus it is entirely authoritative, and the reference to the UK took away from your own argument.

I submit it is a valid point that Gabriel's declaration might boost the migration wave further, even if we might differ about the magnitude. But, more importantly, I think there are other factors which reduce its significance:

• You are right to emphasize the role of communication in creating a snowball effect, but IMHO the strongest part is not what politicians say. In the dozens of interviews with the refugees I read, when telling about the target country, almost every single one mentioned some relative or friend who already made it there. Unlike the comments of politicians, which most of them know only in the most superficial second- third- and n-th-hand form, what personal acquaintances say is direct and detailed.
  
• Meanwhile, there is another public opinion to address: the German one. Up until now, large parts were oblivious to the task of absorbing 100,000 a year, and it will be much more this year whatever Gabriel says. I think quite to the contrary of what you say, this time Gabriel was looking ahead and wanted to make a large refugee influx the new norm in people"'s minds.

_{*Lunatic*, n.
One whose delusions are out of fashion.}