There's no such thing as a "sure thing" on an animal. Deer can practically turn inside-out even at close range. 50 yds adds a variable, but if you wait for a perfect, fool-proof shot...you are never going to take a shot.
That said, I've passed on deer that were very close because the situation wasn't right. For me to take a 50 yd shot, everything would have to feel right...but if it did, I'd take it.
I'd also add that attitudes will vary some between people who get to spend an entire season hunting elk every year and the cost is minimal vs. people who might get to go for a few days once or twice in a lifetime and spend thousands of dollars to make it happen.
Last thought...where do you draw the line? What's the difference in an "iffy" shot at a squirrel, or rabbit, or carp, or gar, or stingray, or whitetail, or elk? As far as squirrel, or rabbit, or carp, or gar, or stingrays...I've missed more than I've hit. I dare say pretty much anyone who's hunted them has. Should we wait on a more perfect shot on these also? Why or why not? Just something to mull over.