I'm not talking about things like the Dakota Access Pipeline, because that one was also guilty of being built across native land without permission. I am referring to pipelines that are only guilty of carrying oil, and possibly leaking it.
What is the point of protesting these? Yes, they carry oil, which pollutes the atmosphere when it's burned. I agree that that is bad. But if the pipeline isn't built, the oil will still be shipped via rail, so you won't be putting a dent in the amount of oil being burned. To seriously reduce the amount of pollution due to burning of fossil fuels, you need to overthrow your country's capitalist regime, and implement a plan to eliminate all power plants and cars that burn fossil fuels in X years. That's the only way that it will work.
Telling individuals to swap their gas cars for electric ones won't work, because most countries, barring China, don't have electric cars that the average person can afford, and those who can afford them don't give a shit. Plus, if the electricity the car runs on is generated at a fossil power plant, then the whole point is moot. And if you're thinking of instantly banning all gas cars and instantly shutting down all fossil fuel power plants, then that will immediately tank the economy, transportation, and the quality of life. Everyone will now hate you, and they will either vote you out, or overthrow you, to replace you with someone who will turn the lights back on. Now you're back to square one, since they're using fossil fuels again. A gradual transition to a clean infrastructure is the only way to actually end fossil fuel use.
So, if that's what you want, then you should be protesting the government for failing to make this transition, and using that as a selling point for revolution. Not protesting individual pipelines.
The other reason I see people protesting them for is oil spills. But they don't realize that the alternative to shipping oil by pipeline is shipping it by rail car, which is even more prone to spilling (source). Before anyone says it, yes, I'm aware that Fraser Institute is a conservative think tank. But the numbers don't lie. So if they're trying to reduce the amount of oil spilled by getting rid of pipelines, they're being counter-productive, because that shifts that oil onto rail cars, which are more prone to spill than pipelines. So, unless there's something else that I'm missing, there's absolutely no point to protesting individual pipelines.