Did anyone say that all toddlers should never be let out of their strollers in public? I don't think so. The PP talked about people having to dodge wandering children at DL. It's a matter of degree and individual situations.
The difference tho between an adult staying out of an adult's way and an adult having to deal with a child running around is that you can see an adult easier than you can see someone knee high who's oblivious to what's going on around him/her. Not to say there are never rude and oblivious adults out there. And you said the bigger safety issue is the adults running through the park...all the more reason not to have a toddler loose to get tripped over.
I will take my 22 month old DGD to the soccer field this week when she visits, and let her run around like a nut, but I will be taking her during the day when school is in session. I will
not be taking her after school when there undoubtedly will be soccer practices going on, as I learned quite quickly one weekend when I brought her to the playground at that same park that swings aren't as interesting as flying soccer balls during games. We left quickly.
So just as being loose at the soccer field depends on the situation, so does being loose at WDW, or DL, or anywhere else.