Why did Luther curse those who oppose indulgences? In the 95 Theses, Luther makes a stand against corruption in the Catholic church of that day. This resulted in events leading to the separation between the Catholic and Protestant churches.

It seems the theses are always referred to, but never actually read. Their content does make me a bit uneasy, especially this part (the English translation used as source):


  71: Let him who speaks against the truth concerning papal indulgences be anathema and accursed.


Or, the original for those that know Latin:


  71: Contra veniarum apostolicarum veritatem qui loquitur, sit ille anathema et maladictus.


Now, I have never heard even one Protestant speak positively about indulgences. What are Luther's motives in saying this (especially in such strong words), and did he later on change his mind?



Edit: Thanks to Caleb's suggestion, I'll add some other relevant theses to provide context.


  67: The indulgences which the demagogues acclaim as the greatest graces are actually understood to be such only insofar as they promote gain. 
  68: They are nevertheless in truth the most insignificant graces when compared with the grace of God and the piety of the cross.
  
  91: If, therefore, indulgences were preached according to the spirit and intention of the pope, all these doubts would be readily resolved. Indeed, they would not exist. 


It seems quite clear to me that Luther didn't oppose indulgences per se, rather just the sale and abuse of them and the exaggeration of their power. If I'm wrong here, please provide some good references to show that.
Why did Luther curse those who oppose indulgences? 

Firstly, he did not curse those who opposed indulgences. He himself was against indulgences. He wrote the 95 theses because of the sale of indulgences:


  Luther, aflame with indignation, challenged the sale of indulgences and demanded that the entire matter be discussed by the scholars of the University. He invited his academic colleagues to a public disputation to consider the Ninety-five Theses, or objections, which he had raised against the sale.


What he said in his 71st thesis, was this "Let those who oppose the truth about indulgences be anathema and accursed". He didn't say "curse those who oppose indulgences," but rather "curse those who are against the truth concerning indulgences."

The "truth about indulgences" was that you cannot buy your own salvation, and Luther was trying to state that. This can be seen in Ephesians 2 : 8,9. 

Now, the Catholic priests and pope were trying to oppose this, by saying that what Luther was teaching was false. Thus, Luther says, "those who oppose the truth about indulgences be...cursed". He was cursing the priests and the pope!

Why? Isn't this rather strong? 

Consider this. When you get someone who deceives others concerning their salvation, telling them that by paying money, they can save themselves, this person is basically sending the poor gullible people to their damnation. They are systematically dooming people with their sell of indulgences. Isn't that what Satan is actually doing? Trying to draw more people into Hell?

Thus, Luther has good reason to curse those who try to oppose the truth of the indulgences.