If I ever see or hear the words "you are voting against your interests", my response is this:
So tell me what my interests are.
The person making the initial assertion will either need to know me very well to accurately assess how I should change my voting patterns to align with my interests or they should admit that they do not actually know my interests.
And if they admit this, then how can they state that I am voting against my interests when they do not have knowledge of them?
I have stated before that "we want the same things" is not often true when it comes to politics. I will state another thing: even if two or more groups with different political idealogies want to achieve the same outcome, vague or specific, this cannot be a source of unity because of the different means that each group will want to use. The real dividing factor here would be implementation of the goals, and you cannot unify on implementation when your plans work against each other.
One example of "wanting the same things" not working out is due to the definition of "the same things" being too vague.
"We want everyone to have a better life."
What does that mean? The answer depends on the ideology of who you ask. The more socialist/progressive minded individual may want incomes/wealth to be evenly distributed, while the more libertarian/free market individual may want everyone to just not have poverty without a care for equity.
Another point to debate is how different approaches to solving a problem cannot be rectified just because "we want the same things."
Let us say that everyone can agree that poverty is bad and we want less of it. How do we end it? The left may advocate for wealth redistribution in many forms, while the right may advocate for less government intervention. It should be clear that these two solutions cannot work together, since wealth redistribution is the government intervention the right opposes.
And this does not even get to the topic of what works and what doesn't. That is often where the debate truly lies, because we still have this debate when everyone is not on the same page about what works and what does not work.
You cannot get the people who want government to do more to have an agreeable solution with those who want the government to do less. The same goes for you cannot get agreement when two or more factions want the government to act but in divergent ways.
The pro-stability rightwing individual would want to see people fall in line with the rule of law. They may not like income inequality or poverty, but those concerns are lesser priorities to them.
While I may have oversimplified the outlooks for brevities sake, the point is that unity is not found in "wanting the same things" if you have not clearly defined what that even means.