Being hammered at sport is naff all to do with safeguarding. If individual leagues etc want to have a rule that games are ditched after a 10 goal deficit is reached, then fine so long as it's in the interests of "sport" and also because it's actually by then a pretty pointless exercise as far as "sport" goes. The world however doesn't run on feelings and kids should learn that sooner rather than later. Competitive sport is ultimately about being better than the other guy/girl/team.
Being hammered 18-nil might not feel very good, but there's little or no difference to being hammered 10-nil and having the referee/teacher have to stop the match because the other team is just going to hammer you more if they don't. The effect is the same. (IMO of course).