What is to stop these wicked angels doing what JW's believe that angels did before the flood?, Most of the posters did answer this question. Read Villagegirls post.
Maybe
Because the last fallen angels could care less about sex they are disturbing every part of the earth. World events and what is on the daily news. Just a guess how JW would answer. Maybe a legend of fallen angels enjoy living inside one human. Maybe they are the cause of why humans choose to shoot down a plane! Or suddenly someone does something they would normally not do. Maybe Satan roams around getting faithful ones to turn against Jesus Christ and using anything he can. Just like in Jesus days. Satans invisible powers are so strong his invisible presence can change a person against another! entices Evil spirits thrive on getting humans to hate one another. Faithful Christians understand that their are wicked forces that are invisible. The war between good and evil is understood in all Christian sects and not limited to JWs.
and why send them here?
Asking Christians why send them here is like doubting Gods judgement upon the fallen angels.
Faithful Christians do not ask why because they believe. I am just stating that the majority of followers do not need to ask why God allowed something because it is their faith in God's judgement that they believe.
I really think many answered your first questioned.