Some commentators reason this as: ’you are the Goddess Lakshmee, an inner-ruler in all beings... (1) though Dasharath was uninterested to select Bharat you made Dasharath, as his inner force, to select a spineless Bharat, and Bharat was established on the throne by Dasharath, through you...(2)  besides, though Dasharath was disinterested to send his dear eldest son Raam to forests, you as Dasharath’s inner force made him to send Raam to forests - his the eldest, the best, and the only ruler of people, namely Raam, [as said in Vishnu’s Thousand names] to forests for the elimination of Raakshas, and thereby releasing us from our accursed being... hence you, as inner force of everybody has to come with me, if Raam’s incarnation is to yield its results."

At that time Vishnu promised to save them from this Shaap Himself. They were born on Prithvi three times and Vishnu also had to incarnate four times. Vishnu saved Hiranyaaksh assuming the form of Varaah Avataar, and Hiranyakashyap assuming the form of Narasinh Avataar in Sat Yug. He was born as Raam and saved Raavan and Kumbhkarn in Tretaa Yug. He incarnated as Krishn to save Shishupaal and Dantvakra in Dwaapar Yug.

Since Raavan was Jaya, many commentators argue that he was a great devotee of Lakshmee Jee, that is why he blames Seetaa for all this episode from the very beginning, because according to Raavan, Lakshmee is the inner-force in everybody's heart and She worked in the interest of Raavan from the very beginning - right from Raam's going to protect Vishwaamitra's Yagya, receiving many kinds of weapons, facing Maareech but not killing him [maybe He knew that He had to see him again], then Dasharath's right to coronate Raam  but still not being able to coronate Him [he could have exercised his authority, but he did not], Kaikeyee's asking of Var at the same time and that also Bharat's kingdom and Raam's exile [it is well-known that Kaikeyee used to love Raam more than Bharat], then Seetaa's coming along with Raam to forest.

Even their coming up to this point of the forest [otherwise they could have gone back to Ayodhyaa easily after spending their 14 years of exile just staying outside their kingdom] was also because of Lakshmee Jee. Arising the desire in Raavan's heart to abduct Seetaa which resulted Raavan contacting Maareech, forcing him to lure Seetaa in the form a Maayaavee Mrig, sending Raam far from Seetaa, then Maareech crying in Raam's voice "Haa Lakshman, Haa Seetey" to create the perfect environment to abduct Her - everything was guided by Lakshmee Jee.

"Although I am your foolish servant but grace me too as I am your long serving servant. Raam is not fallen from kingship. When He is the king of Trilok why should He care for such a kingdom. You are in love with Him, I have no objection in that but bless me too. So please come with me to Lankaa so that He can follow you and accord me salvation as planned by you all."

He pleads and pleads Seetaa to be his wife (to whom he will give the highest position being Lakshmee) so that he can instigate Raam to come to Lankaa and to take His Seetaa back. But when She doesn't heed his pleading, he knows what to do. He abducts Her forcefully still respectfully.

Although Raavan is a wicked soul and of very lusty nature, but he is lusty only for other women, not for Seetaa. He never even touched Her after Her abduction.

(1) One is that this Seetaa had to be sent away from that prospective battlefield, because Seetaa is not trained for warfare that Raam's third mother Kaikeyee had.

(2) Secondly, we see no killings or slayings in Raamaayan in the presence of Seetaa, because She, as Lakshmee, condones any sinner and accords salvation to him or her. As such there might be a probability of Her hindering the war which Raam never wanted.

(3) Thirdly,  Lakshman is an intolerant of any assault on his brother or sister-in-law and may colloid head-on with the aggressors and that may lead Raam up to Lankaa to confront even Raavan. That is the snaky aggressive nature of Lakshman. At that time Raam didn't want to do this so He sent him also away before any further dialog occurs between them.