this started as a comment, but got so long I decided to make it a diary.
The starting point for me is basically, you have to start somewhere. I've been involved in several long-term campaigns against powerful entities (mostly based on environmental issues), and they're usually not very pretty or pleasant. In some ways, they're equivalent to the presidential election battles between the Dem and Rep candidates, without a powerful organisation supporting "your" candidate.
So let's start with a hypothetical environmentalist or environmental organisation in the US. Let's presume that you believe that market forces (eg higher prices for gas/oil) can help initiate significant environmental change. That's a pretty realistic assumption.
You are aware that
-Alberta tar sands extraction is extremely wasteful, in that it requires much more energy to extract than conventional techniques.
-Alberta tar sands extraction is significantly more damaging than conventional techniques, in terms of air, surface water, and groundwater pollution.
-Alberta tar sands extraction is being developed as an alternative to conventional oil sources, which are being tapped out.
-Special interest groups affiliated with the Keystone Pipeline (eg the Koch brothers - http://www.nakedcapitalism.com/...) have thrown enormous amounts of money at attempts to influence US politics, and have waged a massive misinformation campaign.
Since you're based in the US, you don't have much influence over Canadian politics. But the Keystone pipeline is running through the US. Even if you don't have a realistic expectation that you can stop the Alberta tar sands extraction, you realize that you can use the Keystone pipeline for leverage.
Campaigning against Keystone provides you opportunities to:
-Build public awareness and support on the issue.
-Build partnerships with other organizations, communities, and interest groups.
-Get involved in local, state, and national politics on the issue, and show support for finding more environmentally responsible energy solutions.
-Do fundraising to support the work you do.
-Wage an attrition campaign against the Keystone pipeline champions/funders, by slowing, stalling, or stopping the project.
And the alternative? Sit back and watch it happen, because it's going to happen anyway. I was going to write more here, but it would just be sarcastic.
What confuses me about reactions by people who think it's useless, is why bother telling people that their work is pointless? If this is going to happen anyway, why spend any energy informing people of the inevitable? What are you looking for?
I'm somewhat sympathetic to this perspective, because when I was younger, I spent a lot of energy looking for perfect solutions. I'd get involved with activist groups, and mostly contribute by providing what I considered to be constructive criticism, bringing up possible secondary and tertiary impacts, pointing out flaws, and so on. It took a long time for me to realize that I wasn't being very useful, because I wasn't really involved. I wasn't moving anything forward, I was just telling people who were actually doing things that what they were doing wasn't perfect.
It took a long time for me to move towards a place where I'm actually doing things. I often get "helpful" advice from people - I usually listen patiently, on the chance that I can direct their energy towards useful work. Sometimes it works, sometimes it doesn't. After awhile, I tune them out, but keep the door open - if they come to a place where they're ready to work constructively, I'm happy to work with them.