Do the people who dislike Vivienne for her lack of empathy also dislike Sera for the same reason? She dislikes mages too, and also thinks they should be locked away with their scary magic.
Yes, same reasons I dislike Sera. Though Vivienne gets points for turning Sera's pranks back on her at nearly every turn. She shuts her down at nearly every turn. I have to admit, I think its a riot when she does.
...skitter, skitter... 
Ahem...
Again, I don't disagree that there need to be safeguards. We've got people who can burn down cities with their minds. Templars ARE needed. However, Tranquility is dangerous. Ameridan tells you this when you meet him. It is NOT a mercy, it's mind rape. Killing them is merciful in comparison. It's use has become so familiar that it is used when there is a disagreement, and the mage can only protest or fight back. Cullen tells you that Meredith had some mages branded for really petty reasons. No trial, just bye bye free will.
However, for every Meredith, Alrik, and Lambert there is a Greigor, a Rutherford, and a Barris. There ARE good Templars who know how to handle mages, and know how to protect them from others and themselves. Not ALL Templars are bad...and not ALL mages are good. I simply see Vivienne as falling into the bad camp. IMHO, ya know? That's me. Others do NOT see it that way. They see her as practical, and pragmatic. Which is fine. Everyone is entitled to their opinion. It's why I switched from Final Fantasy to Dragon Age. Can you imagine her in that game? She'd either be a straight up villain, or she'd be fawning over the main character at every turn. 
As I said, I love to hate her. She's complicated, ruthless and dangerous. Thank goodness for that instead of bland shonen garbage that we could have been shoveled.