I am not a parent, yet..But to me if a parent has to resort to using leash, they must have a very good reason to do so..Ts were comparing to his old days, where parents does not use leash to control their kids..Well, in the old days there is this thing that is called a CANE, atau dalam bahasa malaysia ia dipanggil sebagai ROTAN..In the old days, parents use this 'ROTAN' to educate/discipline/control their stubborn kids(I did not say all parents use it, but some did). If you were a Muslim, you may see these "ROTAN" more frequently(ustaz use it to point at the Quran, and ask student to read the line..)

So is that parent/ustaz act inhumanely by using 'ROTAN'??I dont think so..

Basically its all about why you use it(rotan,leash, etc..). If it is one of the method for parent to control and avoid their kids to get harmed, then it is okay to use it when it is absolutely necessary(I am not saying that is is absolutely okay to use it, just when the condition needs it). However, as to your point if the parent use it so that they can have their own time doing unnecessary things(FB, chatting etc..), than I can agree with you that it is wrong for the parent to do so..

ps; am not a parent but I do took care of my nephews once in a while before(all of them grew up already)