Does the belief in intercession have any roots in Islam?

One of the beliefs of the Twelver Shiites is the belief in intercession. They maintain that a sinner under certain conditions may be granted forgiveness by God through intercession.
The Wahhabis have raised questions against the Shiites regarding this belief. They say that having such belief leads man to not fear God and be inclined to commit sins relying on intercession. But the truth is that not only intercession does not make one inclined to commit sins but also it prevents him from it.
For intercession to take place there are several conditions. One of them is that there should be a harmony between the intercessor and the one on behalf of whom is being interceded. As long as the sinner feels no shame in disobeying God and does not try to repent and compensate for his wrong doings he will not be eligible for being interceded on his behalf.

Anyone studying about intercession will find that:

1- The act of intercession will take place only if God permits it:

“Who is it that can intercede with Him except by His permission”?[1]

2- It has several conditions for example it is only for those with whom God is pleased:

“and they cannot intercede except on behalf of one whom He approves”.[2]

3- The intercessors will not intercede on behalf on one who is careless of God’s rules, for example one who does not attach importance to prayers. Imam Sadiq (as) in his deathbed said:

“Anyone who belittles prayers will not be included in our intercession”.[3]

4- It does not guarantee the redemption of any specific person. Thus no one can rest assured that he will be saved through intercession but he is always in a state of hope and fear. He is neither so fearful resulting in disappointment and nor such hopeful resulting in negligence and carelessness.
5- The time and place of intercession is not known, whether it will be in the purgatory world or on the Day of Judgment. It must be added that on the day of resurrection man should go through many stages each of which may take very long time. 

Footnotes:
[1] 2:255, مَن ذَا الَّذِي يَشْفَعُ عِندَهُ إِلَّا بِإِذْنِهِ.
[2] 21:28, وَلَا يَشْفَعُونَ إِلَّا لِمَنِ ارْتَضَىٰ.
[3] Kafi, Vol. 3, p. 270, إِنَّهُ لَا يَنَالُ شَفَاعَتَنَا مَنِ‏ اسْتَخَفَ‏ بِالصَّلَاة