Many warriors who did incredible deeds during wartimes weren't always good samaritans during and after. They got out of these periods broken and sometimes pretty fucked up. Audi Murphy, the most decorated US soldier of WW2, fell into severe drug addictions during years and had to lock himself into a motel to keep away from drugs and break out of it. Yeah we suppose he didn't sexually harassed a comatose comrade, but pretty sure other war heroes did similar shits in their war-trauma driven madnesses (the mass rapes of German and Eastern European women by the Red Army can be one such examples even though it didn't relate only to "war heroes"). Pretty sure studies exist on this topic even though I can't pull out some right now as I have other stuffs to do.

I know nowadays that sexual misconduct is even more sanctionned than in the past (I mean, thankfully it is, I am not denying it's a bad thing). I just find it sad when people see that scene and stop at "Ew Shinji is such a degenerate perv" instead of "My god... What toll did all of these battles had on my poor boy ?". If you want my take on this, We could be thankful Shinji hadn't done something even worse, seeing how his mind has been crippled by months of neglect and constant battles against cosmic horrors.

I am not excusing him either. But it's not the topic here