I can totally point out that in similar situations, the result was a market failure, and that it might be good to do something about that before it happens agai

I can totally point out that in similar situations, the result was a market failure, and that it might be good to do something about that before it happens again. Now, to put up a straw-man against that, why not wait to see, usually these platforms fail pretty quickly anyhow? Well, if the outcome is either failure of the platform, or success of the platform by capturing (nearly) all of the market, then why no regulate it?