Given that currently we a Shipping the oil by train/truck its not only more economical, but I would think safer to ship it by pipeline. Given the destruction of Lac Mégantic and that was largely oil containers that exploded, that would serve as a powerful and tragic illustration as the danger derailment poses.
But the debate of keystone isn't about the safe or environmental impact. As much as they debate those points. This arguement is large about climate change and NIMBYism. Climate change(CC) Environmentalists are opposing this because its oil, and CO2 climate change. But those point aren't as salient as they once where so they've changed it the oil spills and tar sands. It's more economical in both in cost and in carbon footprint to ship by pipeline. But CC environmentalists are more interested in a idealogical argument rather than a practical arguement, and they 100% against anything oil.
Most people aren't idealogues, they are pragmatists. So when it comes to climate change they become disengaged, because many of the requirement to deal with climate change, are too costly or arduous. CC environmentalists aren't able to address the source of the problem, the high demand for oil. So Instead the focus on the dramatic, Tar Sands, oil spills, apocalyptic forecasts etc to achieve their agenda. They want to make thing as costly as possible. So they go for oil companies, because big oil is much easier to target than average joes. Regardless of what environmentalists say or do the price of their actions are always felt by the average person and not by the companies. Either at pump, with jobs, with day to day items becoming more expensive.
There's an enonomic arguement to be made for doing that. Increasing the cost of oil, should result in a decrease in consumption. But oil is a product insensitive to changes in price. As much as we complain about the price of oil people will pay what they need to pay, We have a society that is far more dependant on it, than one should ever be. The focus of any debate should be on reducing our consumption, but unfortunately its not.