they proably would have, but with Tree Diagram out of the picture, it would be impossible to interprit the data. Plus, from what I hear
Just because the Experiment itself was secret, the fact that Accel lost to a Level 0 was not. Rumors have a way of spreading around.
and about them suddenly beginning to attack him, I see it like this:
People regularly attacl him and he defeats them, but when the news that he lost, and may not be the stongest spread, all those people that were too scared to fight him before got a confidence boost and decided to give it a go.
And why wasn't Touma targeted? He may have been. Infact, unless I heard wrong, he went on the beach holiday in Vol 4 to gat away and let the situation calm down because of this. Plus, the fact that he was the one to defeat Accel prob isn't common knowledge, just that it was a Level 0.