Here's my take on this.

0-80% of players flame

No. That is a lie and that bull statistic alone made me want to stop reading right off the bat. It is closer to, maybe 1-2% being ban worth, 5% AT MOST. I would say I encounter someone who I report for harassment maybe one in 10 games? Around that.

And as for your

250 hours of Dota experience it actually bonds a team together

I have found the opposite. I don't play much Dota, but my roommates do and I played a lot of HoN back in the day. From my HoN experience, voice chat made me hate the game. All it did was spread toxicity so horribly, it was just frustrating. Yeah, you can mute in the same way you can mute ragers typing in the normal chat, but theres something about an actual human voice harassing you that makes it worse. It's no longer just text.

As I said, my Dota experience is much more limited, but from my experience there and watching my roommates play, it feels like someone always gets mad every game. Whether it's a guy who is younger/has a feminine voice being called gay, a girl being harassed or a guy with an accent being told to "go back to Russia/Mexico/etc". Maybe it's just from my limited experience, but I've played about 20~ games myself and watched a bunch with my roommates, and honestly it just turns me off from voice chat.

The thing with Curse Voice is that the people who go out of their way to download Curse Voice and use it are the type who want to communicate. When something is a right, people abuse it. When you have to work for it, people respect it more.

All of this is from my (anecdotal) experience though, so take it with a grain of salt.