Climate change is like having your kitchen on fire, and being against pipelines is like being against having a direct, flammable connection between your stove and your bookshelf. Obviously you want to preserve the Twilight collection as long as humanly possible, but just removing that connection isn't going to prevent the whole house from burning down. We need to stop throwing gas on the fire.
Stopping pipelines from being built does nothing to actually curtail the production of fossil fuels. So, the problem with halting pipeline production, with no plan in place to reduce fossil fuel production, is that this implicitly favours the transport of oil and gas by rail. Which doesn't leak as much, but does occasionally kill people.
Between 2004 and April 2017, in Canada, there were 1536 reported pipeline "incidents" (including leaks of oil, gas, and other hazardous materials) and zero of them are reported to have caused human fatalities or even serious injuries.
In that same time, in Canada, there were 3106 reported accidents involving trains carrying "dangerous goods". Out of those, 9 led to serious injury and 3 led to a total of 49 fatalities (47 of which were in the Lac-Mégantic rail disaster).
So, if the plan is to just stop pipeline construction, and not actually curtail fossil fuel production, then we're just opting for rail, which is a more immediately dangerous, albeit slower, method of moving fossil fuels.
NOTE: when we do build pipelines, we still need to be careful where they are built. Clearly, it's a problem to build them on sacred land and/or dangerously close to water supplies.