I don't really find this argument convincing. If you define "pragmatic" as "instrumentally rational in achieving their preferred policy ends," then it's true that the Sincere Moderate is not more pragmatic - they just have different goals that happen to be easier to achieve. But I don't think any Sincere Moderate is claiming to be pragmatic in this way. Rather, they think it's their policy ends themselves which are more pragmatic. After all, no one really supports any policy as a terminal goal. We all support policies that we think will be able to achieve our real goals. A Sincere Moderate thinks overly ideological policies are bad at achieving the shared goals people really care about, and therefore, a moderate policy agenda is more pragmatic.
As for Self-Effacing Extremists, there are actually three ways to disagree with them. The third is to know that an extreme agenda is doomed to fail and that advocating for it will increase the probability of a catastrophic outcome, but choosing to advocate for it anyway. This is clearly instrumentally irrational, and there are abundant examples of people like this (see, for example, pro-Palestinian protestors who want to make Harris lose the election even though Trump is worse for their cause). The argument that anyone who disagrees with the Self-Effacing Extremist must do so because of (1) or (2) assumes from the beginning that everyone is instrumentally rational enough to act as consequentialists, but a lot of people aren't.
But even if a true extremist disagrees with the Self-Effacing Extremist because of (1) or (2), that doesn't mean that they are just as pragmatic as the Self-Effacing Extremist. Ideological extremists, like all people, suffer from motivated reasoning. In particular, they are motivated to believe and try to justify the conclusion that their agenda actually has some hope of success and that advocating for it will make it more likely to succeed, rather than help the people who want the opposite of their agenda. After all, there's a lot of cognitive dissonance involved in, "I believe X, but I can't advocate X," even when refusing to advocate for X is the most rational thing to do. But engaging in this type of motivated reasoning is instrumentally irrational. It's no defense of true extremists to say that given their goals *and their practical beliefs about how they can best achieve their goals,* their actions are not irrational. After all, the practical beliefs can be irrational. The difference between an idealist and a pragmatist is that the idealist has an overly rosy picture of how easy it will be to achieve their goals, or they believe that they can achieve their goals without doing anything they find distasteful (like compromising with the other side). But that's exactly the difference that you point to here as a supposed proof that extremists aren't less pragmatic than moderates.
With regards to the incrementalists, you didn't really give an argument for why they're not more pragmatic than extremists. "They might be wrong," can be applied to any claim, and incrementalists have arguments for why they're right. If you want to show that they're not more pragmatic than extremists, you would have to evaluate these arguments, or provide evidence that extremists are actually better at achieving their aims than incrementalists.
I don't really find this argument convincing. If you define "pragmatic" as "instrumentally rational in achieving their preferred policy ends," then it's true that the Sincere Moderate is not more pragmatic - they just have different goals that happen to be easier to achieve. But I don't think any Sincere Moderate is claiming to be pragmatic in this way. Rather, they think it's their policy ends themselves which are more pragmatic. After all, no one really supports any policy as a terminal goal. We all support policies that we think will be able to achieve our real goals. A Sincere Moderate thinks overly ideological policies are bad at achieving the shared goals people really care about, and therefore, a moderate policy agenda is more pragmatic.
As for Self-Effacing Extremists, there are actually three ways to disagree with them. The third is to know that an extreme agenda is doomed to fail and that advocating for it will increase the probability of a catastrophic outcome, but choosing to advocate for it anyway. This is clearly instrumentally irrational, and there are abundant examples of people like this (see, for example, pro-Palestinian protestors who want to make Harris lose the election even though Trump is worse for their cause). The argument that anyone who disagrees with the Self-Effacing Extremist must do so because of (1) or (2) assumes from the beginning that everyone is instrumentally rational enough to act as consequentialists, but a lot of people aren't.
But even if a true extremist disagrees with the Self-Effacing Extremist because of (1) or (2), that doesn't mean that they are just as pragmatic as the Self-Effacing Extremist. Ideological extremists, like all people, suffer from motivated reasoning. In particular, they are motivated to believe and try to justify the conclusion that their agenda actually has some hope of success and that advocating for it will make it more likely to succeed, rather than help the people who want the opposite of their agenda. After all, there's a lot of cognitive dissonance involved in, "I believe X, but I can't advocate X," even when refusing to advocate for X is the most rational thing to do. But engaging in this type of motivated reasoning is instrumentally irrational. It's no defense of true extremists to say that given their goals *and their practical beliefs about how they can best achieve their goals,* their actions are not irrational. After all, the practical beliefs can be irrational. The difference between an idealist and a pragmatist is that the idealist has an overly rosy picture of how easy it will be to achieve their goals, or they believe that they can achieve their goals without doing anything they find distasteful (like compromising with the other side). But that's exactly the difference that you point to here as a supposed proof that extremists aren't less pragmatic than moderates.
With regards to the incrementalists, you didn't really give an argument for why they're not more pragmatic than extremists. "They might be wrong," can be applied to any claim, and incrementalists have arguments for why they're right. If you want to show that they're not more pragmatic than extremists, you would have to evaluate these arguments, or provide evidence that extremists are actually better at achieving their aims than incrementalists.