Well I can say that the US dodged a bullet by not accepting mass amounts of refugees into our country without being able to properly vet them -- so yeah, I do think that this was a blunder by the European nations of the world. While not vetting / making sure these people are safe -- you're pretty much ensuring that the worst type of people are being allowed to trickle into your country.
Take this article for example -
https://www.newsweek.com/migrants-europe-violence-crime-germany-study-770105More than 90 percent of the 10.4 percent increase in reported violent crimes was attributed to young male migrants in Germany's southern state of Lower Saxony, according to a new study from the Zurich University of Applied Sciences. A huge wave of migrants flooded into the European Union in 2015 from countries through Greece and Turkey that led to more than one million migrants applying for asylum in Germany.
There's no reason to accept people in with open arms like this while ignoring the fact that they could be corrupting your nation -- I'd much rather have proper vetting and screening to ensure that your citizens are safe.