I don't think it's arrogance. I think it's perfectly fine to proselytize to younger muslims, but would you bother arguing with my 87 year old grandmother who talks to me regularly about how jinns are the cause of power outages in Dhaka? Some people need to be left to their illusions. I have no desire to break sandcastles, what's the point?
That's my perspective too. I have a grandfather who has diabetes and has suffered a heart attack, he's a born again christian and when he tries to invite me to his religion I politely decline without offering any counter arguments.
I have no qualms about debating muslims online or presenting counter-perspectives, people who come online know they will encounter opinions that will challenge them.
Also I genuinely think that the group-think, misogyny, and barbaric laws that are propagated by most muslim sects should be countered, I think it impedes (genuine) happiness, and progress for humanity in general.
I share the concerns of Whabbist though. Leaving people in a vacuum after successfully challenging the foundations of the religious beliefs is pretty inconsiderate IMO. That's why I like dudes on youtube like; Evid3n3, Philhellenes, Thunderf00t, Theramintrees, and Therationalizer they present an alternative worldview (even if only a single vid) to religion alongside their criticisms.
Richard Dawkins and Carl Sagan have done it brilliantly IMO, they both present the wonder and beauty of the universe, and the achievements of rational enquiry, alongside their critiques of magical thinking/religion. It's a kind approach.