I have addressed this particular point so many times, I need to just write up an essay and link to it.
In summary, I have found a lot of evidence to indicate this was just a lie told for propaganda purposes. There was never going to be any significant slave presence in the "territories." It was economically nonviable.
It also opposed returning slaves from the North to the South ...
It could oppose it all it wanted, but as that particular requirement was written into the US constitution in Article IV, Section 2. It was constitutional *LAW* that required escaped slaves to be returned. Look it up.
...and letting Southern slave-owners bring slaved into the North.
George Washington kept a slave plantation in Pennsylvania long after Pennsylvania declared itself to be a "free" state. I will also point out that telling American citizens they could not travel with their "property" was a violation of the privileges and immunities clause of the Constitution. States were required to accept the laws of other states regarding private "property."
But consider why Texas fought:
I looked up your source. It was dated February 2nd, 1861, which I believe was BEFORE the civil war. I'm not going to say you are trying to deceive us, but you may be unintentionally misleading people here. You are offering up a statement from the convention delegates regarding SECESSION, not fighting.
Texas fought because their sister states were invaded. Would you have fought if your sister states had been invaded or would you say "not my problem." ?
So you are offering up a reason alleged by a bunch of convention delegates as to why Texas left but this is different from giving a reason why they fought.
Do you have any statements from Texans who fought regarding why they fought?
Yes, I’m telling you WHY Texas left the Union. SLAVERY - and expanding it and LOVING it was their goal. By their own words.