What does it matter if the person making the argument carefully considered the opinion or not? If not, then it won't be a good argument anyway and will get ignored (just as it would from an adult). If they did, then it will put across another point of view to be considered.

I like the anonimity, it allows a less biased consideration of more points of view and information than it would if you could pick and choose which things to read/listen to or decide how valid it is likely to be before even seeing/hearing the content, (which is precisely what you are saying by the way).