It is irresponsible because the message was sent that everyone could just come and be taken care off, while the organisations in Germany are not capable of processing everyone. Because of the open border policy, people that are not from Syria also went along with it trying to get into Europe and make use of the situation.
This way of doing things also forces people to pass through multiple countries, that do not want that. Now Hungary has closed off, Austria has set limits and it went from border to border because nobody wants to have a large amount of people in their country that have nowhere to go, but also don't want to stay there.
It is also irresponsible to have people make a dangerous journey like this across the sea and continent where people die and get abused by smugglers.
The responsible thing to do would have been to get the people in need from refugee camps and give them a safe way to Germany instead of going "get here somehow, maybe you'll die or get hurt along the way, but look at me being all helpful!"
Germany said "come here and we'll take care of you" but didn't provide a way to actually get there. Now countries like Hungary and Austria have closed off or set a number of people they let in. You can't blame the Balkan countries for blocking people, since otherwise they would be stuck there. Macedonia gets made out as being the bad one and stopping refugees, but if they let them through they would have the same on their border with Serbia.