For the most part, I think that the outside world's view of the practice of sati is a negative one. Europeans, in particular, could not fathom the practice, and could not embrace the idea of it. Certainly, as women's rights became more of a dominant theme at about the time when colonization and imperialism were on the rise, these values were applied to India, causing a fairly instant rejection of the practice. Consider a French emissary's view of it in writing about what he experienced in witnessing it:
Well indeed may I despair of representing this whole scene with proper and genuine feeling, such as I experienced at the spectacle itself, or of painting it in colours sufficiently vivid. My recollection of it indeed is so distinct that it seems only a few days since the horrid reality passed before my eyes, and with pain I persuade myself that it was anything but a frightful dream.
To a great extent, the Western and non- indigenous view of the practice helped to foster the belief that those who engaged in the practice were "savage," necessitating foreign influence in order to "civilize" them. I think that it should be noted that while the practice itself is difficult to defend, and few, if any, would, the European and foreign rejection of it is not a justification of the imperialism and colonization that resulted. It might just be that this is one of small handful of areas where the Europeans or outsiders "got it right" in criticizing the practice.
I would also suggest that it is really difficult to find any text from the Hindu religion that specifically advocates the practice. The practice of sati is something more rooted in cultural tradition and a sense of bias against the view of women, and not something immediately sanctioned in the Puranic texts. This divergence between what is stated in the religion and what is done through cultural practice is one of the reasons why Indians, Hindus included, view the practice with skepticism and not one with embrace. I think that the larger issue present regarding non- Hindu views about the practice relate more towards the idea of power and the ability to exercise it, more than anything else. The practice became one of many issues where people claimed to have spoken for women, but might have been doing it for their own consolidation of power more than anything else.