As of 1861 they were a numerical minority to the extent that the north could run roughshod over them and impose whatever rates it pleased. That one has a voice in the court of a tyrant does not reduce or alter the fact that he engages in tyranny.
And if the taxes had to be increased, then the other southern states could have pulled out?
In 1861 they were increased and they did pull out.
what rate does triggers this massive secession?
It's contingent entirely upon the individual circumstances of the case. You might as well be asking what rate on tea is necessary to trigger the Boston Tea Party and make it something different than any old mob riot.
Yes, they have the power do so and the power comes from an implied right,
Rights are inherent, not implied, and the power to tax is by no means a right. Governments tax only upon the consent of the governed, or so says our claimed theory of government. When they abuse that consent and tax excessively then the governed have an inherent right to deny their consent.
The Democrats still had enough votes in the Senate to block anything of that nature.
Below is the speech from Alexander Stephens, against secession
But it is said Mr. Lincoln's policy and principles are against the Constitution, and that, if he carries them out, it will be destructive of our rights. Let us not anticipate a threatened evil. If he violates the Constitution, then will come our time to act. Do not let us break it because, forsooth, he may. If he does, that is the time for us to act.
(Applause.) I think it would be injudicious and unwise to do this sooner. I do not anticipate that Mr. Lincoln will do anything, to jeopardize our safety or security, whatever may be his spirit to do it; for he is bound by the constitutional checks which are thrown around him, which at this time render him powerless to do any great mischief.
This shows the wisdom of our system. The President of the United States is no Emperor, no Dictator-- he is clothed with no absolute power. He can do nothing, unless he is backed by power in Congress. The House of Representatives is largely in a majority against him.
In the very face and teeth of the majority of Electoral votes, which he has obtained in the Northern States, there have been large gains in the House of Representatives, to the Conservative Constitutional Party of the country, which I here will call the National Democratic Party, because that is the cognomen it has at the North.
There are twelve of this Party elected from New York, to the next Congress, I believe. In the present House, there are but four, I think. In Pennsylvania, New Jersey, Ohio, and Indiana, there have been gains. In the present Congress, there were one hundred and thirteen Republicans, when it takes one hundred and seventeen to make a majority.
The gains in the Democratic Party in Pennsylvania, Ohio, New Jersey, New York, Indiana, and other States, notwithstanding its distractions, have been enough to make a majority of near thirty, in the next House, against Mr. Lincoln.
Even in Boston, Mr. Burlingame, one of the noted leaders of the fanatics of that section, has been defeated, and a Conservative man returned in his stead.
Is this the time, then, to apprehend that Mr. Lincoln, with this large majority of the House of Representatives against him, can carry out any of this unconstitutional principles in that body?
In the Senate, he will also be powerless. There will be a majority of four against him. This, after the loss of Bigler, Fitch, and others, by the unfortunate dissensions of the National Democratic Party in their States.
Mr. Lincoln can not appoint an officer without the consent of the Senate -- he can not form a Cabinet without the same consent. He will be in the condition of George the Third (the embodiment of Toryism), who had to ask the Whigs to appoint his ministers, and was compelled to receive a Cabinet utterly opposed to his views; and so Mr. Lincoln will be compelled to ask of the Senate to choose for him a Cabinet, if the Democracy or that Party choose to put him on such terms. He will be compelled to do this, or let the Government stop, if the National Democratic Senators (for that is their name at the North), the Conservative men in the Senate, should so determine.
Then how can Mr. Lincoln obtain a Cabinet which would aid him, or allow him to violate the Constitution? Why, then, I say, should we disrupt the ties of this Union, when his hands are tied-- when he can do nothing against us?
I have heard it mooted, that no man in the State of Georgia, who is true to her interests, could hold office under Mr. Lincoln. But I ask, who appoints to office? Not the President alone; the Senate has to concur. No man can be appointed without the consent of the Senate. Should any man, then, refuse to hold office that was given him by a Democratic Senate?
The South had full representation in Congress.
What they did not like is the trend that was moving away from them in the House and the addition of free states to diminish their power in the Senate, which would have eventually led to limitation of slavery
No one was abusing them with taxation.
http://www.pointsouth.com/csanet/greatmen/stephens/stephens-speech.htm