It isn't necessarily nefarious but can be. Recent events have shown quite a bit of nefarious activity surrounding this practice which is why there is a call for increased regulation.
Any business decision can be nefarious in some context when it's a bad one. At the same time as recent events may call certain buybacks into question, historical events tell a different story.
For example a common argument to ban buybacks is that they were illegal prior to 1982. We also had no good place to park savings before 1982, where at the same time we had seen enormous inflation the stock markets had been on steady decline since the mid 1960s. People weren't just losing money due to inflation, they had fewer options about where to put it reliably.
And when it comes to regulation I don't know what the best way to do it is other than letting companies that made bad buybacks die, or bail them out by diluting shareholders in some kind of bankruptcy proceeding.
