This is only true in flourishing economies. Economies that can't sustain their current populations cannot afford to take on more of a burden. I've referenced this reality when people try to cite the positives of immigration elsewhere in this thread.
Yes, dumping a million refugees on a bankrupt country like Greece - probably not going to make life a whole lot better for them. Dropping a hundred million refugees on Germany would more than overwhelm any amount of economic ability the country has to assist. There is certainly a level of which a country could support and integrate before the load becomes too high.
I believe the military intervention that was imposed in WWII is hard to be quantified as pure loss. I think most would agree if intervention had occurred earlier there would have been less loss. I.E. concentration camps and gas chambers.
Even hindsight is difficult to decide whether WWII was a net good for the world or not. The Axis powers certainly committed their fair share of atrocities, but over the course of the war, something on the order of 80 million people died, and entire cities were leveled. If more countries adopted strict neutrality, would the result have been better or worse? It's really pretty hard to say. Would the eradication of the 9 million European Jews left the world in a better or worse place than the deaths of approximately 24 million Soviets? For that matter, virtually every major conflict in the latter half of the 20th Century can trace its roots back to the outcome of World War 2. It's impossible to say whether an Axis victory would have left the world in a better or a worse place. I don't say that from an antisemitic point of view, but just from the general philosophical point of view that you can't take for granted that millions of lives were lost in the war and it's impossible to know what the other options might have been. Maybe Hitler with a conquered Europe would have given von Braun a blank check and said start colonizing the Moon, Mars, and beyond, and we might have been celebrating the first Martian birth by now - even if their parents did speak German.
What do you believe to be the most conservative estimate for the cost of refugees? Furthermore how long do you believe this cost will go on for?
I'm no economic planner, and the rates are going to be very different depending on what country you're in and what percentage of the refugees are able to work, what percentage are elderly/sick, and what percentage are young and require school. German minimum wage is 1,473.00 EUR/Month. Let's say that would be enough to support a family. Say average 18 months on public assistance before they could be employed and support themselves at a similar level, and for Germany, you'd be looking at 26,500 EUR per refugee family in total. Some are going to need more (say a single mother with 6 young kids probably couldn't do much more than run a day care), some are going to need much less (say someone comes already speaking the language and possessing an employable skill).