Several point to make here Reggie.
1. The views of no one theologian, even Aquinas, may be held in preference to what the Church later establishes.
2. Just before his death, Thomas Aquinas made the following act of faith: "Neither do I wish to be obstinate in my opinions, but if I have written anything erroneous concerning this sacrament or other matters, I submit all to the judgment and correction of the Holy Roman Church, in whose obedience I now pass from this life."
3. Even though Aquinas did not claim that Mary was sanctified from the moment of her conception, he did claim that she was sanctified before her birth,
4. To quote Saint Thomas Aquinas "We must therefore confess simply that the Blessed Virgin committed no actual sin, neither mortal nor venial "
5. Since this dogma was not declared until after his death, Aquinas NEVER taught against the Magesterium.
So to say that Aquinas didn't believe in the Immaculate Conception but neglect to point out he did believe she was sanctified before her birth, is being deceitful.
Deciet is picking and choosing from what he wrote and selecting things you like instead of what lines up with scripture and then selling it as gospel truth. That is deciet. Not to mention the fact that this guy on His best day didn't have even a measure of the authority of the Apostles. Nothing in scripture says that Mary was sanctified from birth - not even close.