Asterina starfish are great, IMO. There are many species of Asterina starfish, with 1 or 2 species thought to pose a possible problem, mainly to Zoanthids. However, I've yet to read any "proof" of this, other than by a dubious source (GARF) who seems to have started the Asterina Scare!
There have been instances where people have claimed that their Asterina starfish were eating their SPS, even providing photo evidence, showing an Asterina starfish on an SPS, them moving off, leaving a bare area of skeleton, with the flesh removed. My opinion is that the SPS was already suffering, on it's way out, and the Asterina was doing what it does, scavenging.
I have literally hundreds of Asterinas in my tanks, and have never had any issues with any of them. I believe, if you were to "poll" the reef community, as a whole, you'd find that the instances of Asterinas causing problems is very rare, and I believe when it has happened, it's due to something other than the Asterina actually being predatory.