I had a problem with the episode which I couldn't put my finger on, until I read the Nitpickers guides..
The whole episode is about stopping warp drive through the area so a rift won't form and cause damage to the planet. So at the conclusion of the episode Serova creates a rift, therefore endangering her planet? That's a bit like saying 'If we put all this dangerous nuclear material here people will die' and then to prove your point, putting it there and killing everyone.
To me that felt like an act of desperation. She was concerned with the greater idea of warp engines damaging the fabric of space-time generally
. Not only that specific region, although the effects were most severe there, because of that narrow corridor everyone had to travel through already.
Desperate to prove her point, she knew that the had to give a demonstration in a region where the effects would be visible at once, which could therefore not be a 'relatively unaffected' region of space. (This is speculation on my part, yes). So region-wise, she had no choice except there. And of course, the TNG crew most probably would have captured here before she could reach another candidate region anyway.
Was it a sane choice ? Don't think so. But someone willing to die herself only to give that demonstration must be viewed either as a person fanatically devoted to a cause , or as a mentally unstable person, anyway. So I don't have a problem with the ep as such for that, as such people do exist.
Just like in the real world, where we have people who could be labeled 'eco-terrorists'. She might just be an extreme example of those.