Opposition has little to do with technical issues specific to the pipeline. It's more big picture environmentalism philosophy that's against this. It's not like we don't have pipelines running all over the country, carrying oil, natural gas, liquids, etc. If people knew how pipelines are built now, they realize how little risk there would be of leakage. They have all sorts of monitoring equipment on these pipes. They take x-rays of each and every weld on the pipe and analyze them to make sure they are up to standard and have those records on hand in case they ever need to dig up the pipes. Etc., etc., etc. People don't want this because it accesses the tar sands, which require a good deal of fossil fuels to access and process, thereby leading to more climate change gasses. Of course if the fuel will be shipped anyway, even if the pipeline isn't completed, as you can send it by rail. Now, that's a lot more risky than a pipeline, but that fact apparently isn't that important to some people.