Re: Ukemi makes you (feel) tougher...
I think the most important part is overcoming the fear of total commitment to following nage, flip-flop or not. But once you know you can do it, it's safer to ease off.
That being said, there are times when nothing else will do. I just think there are less of the times than most seem to think...
Breakfalls are the most athletic part of aikido training, and like all athletic practices, they have to adjust as injuries accumulate and lifestyles change.
It is impossible to be a "tough guy" and a true martial artist. Even if you can flip off an 10 story building onto a bed of nails. If you're a jerk, who cares?