At first glance, you'd think the question that this 1978 cover of What If poses was dealt with on that very cover, asked and answered:
We could also presume that the world wouldn't necessarily care one way or the other about Daredevil's sight or lack thereof--it's really a matter of anyone going up against him knowing that he's sightless, and coming to the conclusion that some other form of perception is at work that makes him such an effective fighter. A well-laid trap sprung later by an enemy, and that's that.
But how did such a secret ever get out, and when? We find the answer in Daredevil's second issue, just as the nascent crime-fighter is getting out of the gate in his red and yellow togs, and facing Electro in the Fantastic Four's deserted Baxter Building headquarters. This time, however, Spider-Man's unexpected entrance into the fray prevents Electro from taking Daredevil by surprise--and when Electro is consequently forced to defend himself from the charging DD, he takes note of something he otherwise would not have picked up on.
The conclusion that Electro jumps to is very selective on writer Don Glut's part, considering that Electro doesn't make the same observation when Spider-Man would later dodge a hurled electric bolt in similar fashion and, like Daredevil, is also unaffected by its blinding brightness. Regardless, a little quick thinking on DD's part, where he could mention, say, special eye slit lenses which shield him from such attacks, is all that would be needed to head off Electro's train of thought. (Artist Alan Kupperberg even has DD pointing to his mask as if to accommodate Glut heading in that direction, though for the sake of the story Electro isn't deterred from making his point.)
And so we return to the world now knowing of Daredevil's condition--and with the exception of the news media capitalizing on such a surprising development, it appears the man on the street is hardly fazed.