I think the migrants are already feeling they are not seen as human beings. They shout out "We are not animals" (yes, I know, all human beings are animals but you get their drift I'm sure). I think in their situation I would not like being described as being part of an anonymous and threatening "swarm".
Of course, these sorts of expressions only fall from usage if more and more people start to think they are inappropriate and that's as it should be. However, it should still be OK for people who have misgivings about using such a word to be able to express that opinion. I think a prime minister, in particular, should be quite careful about the expressions he uses. As durhamjen's link showed, the Swedish minister at least was not particularly impressed.
Nine migrants have died since June - that surely gives some indication of their level of desperation and motivation. Is it possible that they might make a reasonable contribution to this country and show great commitment to it if they are given a chance?