There is no problem if people from any part of country do come to Maharashtra/Mumbai for living. But the problem with people from UP/Bihar is that they want to come here and turn Mumbai into Bihar/UP. And then they blindly follow their great useless leaders like Amar Singh, Abu Azami etc. It would have been ok if these leaders were doing great jobs in their own states. But their states are in dire state. These states are hopeless. And on top of that they come to the stable states like Maharashtra and try to say that all that you have got is because of UP/Bihar people and leaders. This is ridiculous and objectionable.
Violence in any form is not adored but if some leader taunts you continuously and UP/Bihar people continue to express faith in their idiotic laeders very few choices remains for the host state people.
Also maharashtrains are not as hard-core people as being projected in Media. If it was the case then on Marathi card Shivsena would have won all elections till date. But there is limit for everything and so is for patience of Maharashtrans.