What exactly does this strange sentence mean?

Solution 1:

Edsgar Dijkstra is famous for (among other things) writing an article in, I think, Communications of the ACM entitled "Goto Considered Harmful", in which he basically denounced the frequent and careless use of "goto" statements in computer languages such as FORTRAN and Algol.

The line "That Dijkstra is dead is no excuse for using gotos" can perhaps be better understood if you understand that the word "that", in this case, is an idiom of sorts which means "the fact that". Thus the sentence could be read "The fact that Dijkstra is dead ..."

So the sentence is saying that the use of "goto" statements in computer languages is still a bad idea, even though Dijkstra is dead.