The gemara says that K'lal Yisroel were not re'uyin le'oso ma'aseh, they were not really on such a low level as to commit a terrible aveiro as idolatry, elo lehoros teshuvah lerabim, to teach everyone that even for such an aveira, they CAN still do teshuvah.
Perhaps this may be understood as follows: They didn't really have bechira whether to do the aveiro or not. The actual aveiro was not the test that Hashem was testing them with. Rather, Hashem wanted to see what they will do after they were nichshal. Will they just become depressed and dwell in their sorrow, or will they move on and move up?
Lehoros teshuva lerabim, every one of us can think about this point AFTER we slipped. (This is not an excuse to set out on the wrong path, chas ve'sholom.) We can think that maybe, in this case, I didn't really have a bechira in deciding not to guard my eyes. I strayed. I saw. I started slipping. I stumbled. I sank. Now what?? I am worthless. I am a hopeless addict. I am a lost case.... I lost my connection to Hashem. I may as well do another aveiro? ABSOLUTELY NOT!!!!!! Hashem didn't close his eyes. He didn't stop recording. He sees me in my low moments and he sees me as I get up again. Maybe, just maybe, He is the one who pushed me down because he wanted to see me get up. He enjoys seeing me get up from the depths even more than He enjoys it when I coast along at a high altitude without any bumps. So HE PUSHED ME DOWN. Now what? Now I will give him what he wants. I will show him how I get back up!
The above may be alluded to in the gemoro, bemokom she'ba'alei teshuva omdim ein tzadikim gemurim yecholim la'amod. Tzadikim don't give Hashem this specific nachas of getting back up from the depths.
There are times that Hashem takes away our Ruchniyes'dige levels and lowers our gashmius to the depths.... only to see what we will do then!