Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Deliberately looking at a woman and touching her is not permissible except for dire necessity, which is valid in Shariah. Allah Says (interpretation of meaning): {Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.). That is purer for them. Verily, Allâh is All-Aware of what they do.}[24:30].
No doubt, that when merely looking at an alien woman is not permissible in Shariah then touching her would not be permissible either. The Prophet said in this concern: "If one of you were to be stabbed in the head with an iron needle it would be better for him than touching a woman whom he is not permitted to touch". [Sound Hadith reported by Imam Tabrani]
The Hadith of Sahla (May Allah pleased with her) does not prove that the person who had drunk her milk had touched her since it is very possible that she might have put milk in a utensil and from it he drank.
The Hadith of Sahla (May Allah pleased with her) is a sound and authentic Hadith narrated by many eminent Muhaditheen (scholars of Hadith) such as Imams Bukhari, Muslim in their Sahih Books of Ahadith, the four Imams of Sunan in their books and the Imam Malik in his book al-Muwatta. This Hadith is sound and no one from the Sahaba (may Allah pleased with them), their successors and the scholars of Hadith doubted it and did not speak of its content. But, the majority of the Muslim scholars did not make it evidence to approve the validity of suckling a young man. They believe that this was an exceptional case for Sahla (may Allah pleased with her) as all the wives of the Prophet Muhammad (Peace and blessing be upon him) clearly confirmed it except Aisha (may Allah pleased with her). They said that Sahlah and her husband Abu Hudaifa adopted Salim as their son, and at that time an adopted son was considered as an own child. But when Islam annulled this custom she faced hardship and came to the Prophet explaining him that they used to consider Salim as their child so he used to see her uncovered; then the Prophet excused her from this rule to relieve her from that problem, and ordered her to let him drink her milk thus he would be considered her foster son.
But, Aisha (may Allah pleased with her) was of the opinion that this rule is not specific for Salim rather it is general for everyone. Some scholars such as Laith Ibn Saad, Ibn Ulayyah and Ibn Hazam also are of the same opinion.
Anyway, the Hadith is correct and it does not contain any indication of humiliation to the Prophet or his wives.
The Muwatta of Imam Malik is a great Hadith book, which holds high a position among the books of Ahadith. The maximum Ahadith of this book is correct and a few of them are negotiable as the scholars of Ahadith pointed out but these Ahadith do not decrease the great position of this book among the six known books of the Ahadith.
Allah knows best.