Did he force them or did they go willingly? hmm.. what if God cast them out because they were Lucifer's followers? With no choice, they probably have committed sin also, so they were cast out all together.
A better question is this, how did they sin ?
If they had spiritual bodies and were in Heaven, how did they sin? This is a tough question.. since we're going to inherit these spiritual bodies.. since there was no one other than Lucifer that became evil, then how did he become in the first place while being in heaven and in peace.. Did God will it? I don't know.......
Lucifer has I trouble. I will be exalted, I will lift my throne - He wanted to be God. Eve fell for the same trap- you will be like God. As far as the angels and how they sinned it is just speculation but Lucifer must have appealed to their sense of self, their pride and their desire to be exalted. This was the first sin and the root of all sin ever since- the big I, I, I me, me, me.
Well first sin is simply disobeying God.
Second, Lucifer and all the other angels committed the unforgiveable sin. They were witnesses to the glory of God and yet they still rebelled.
The same thing nearly happened to the pharisees; God was in their presence, they witnessed His miracles and they still denied Him and claimed His power was of the devil.
Also, the Bible says that pride entered Lucifers heart and he wanted to be God. He tried to take Gods throne. But our God is awesome and much too powerful to be removed from His throne!!
But my point was how can we sin in heaven.. that's all.. How did pride come into Lucifer's heart :S if he was in Heaven.. I guess spiritual bodies were corruptible ? yet us we're going to be incorruptible, what if we can still be corruptible? Because surely Lucifer was incorruptible, yet he became corruptible, this is strange.. I'm gonna have to ask God about this one when He comes
I recall reeading in Revelation, After the Second Comming, Satan will be imprisoned for 1000 years. then he will be free to raise an army again. and people will come to him once more. This seems to imply that we will still be able to Sin after the end. Or it may refer to just those who were still on earth at the end, and still had physical bodies.
Only those who survive the tribulation and live to repopulate the earth will still be fallen humans in the millenium. The Church will have been raptured and resurrected with their new bodies and will not have to worry about satans last stand at the end.
In fact thats the reason satan has to be loosed for a short time, so that those born during the millenium who have never been tempted, will have the chance to choose God or satan.