SubinDoubt, I echo Callalily's issues with your Dominant's proposed punishment. While I tend to try and kep my own morals and judgments out of posts that aren't about me, I'm afraid I really can't do that here. What your Dominant is proposing, if I'm correct in my assumption as absolutely an unequivocally
wrong. You do not use a limit as a punishment. Ever. Not even a soft limit. A punishment is absolutely not the place to explore these new and somewhat scary experiences. Because a punishment is not a request like other play involving limits is. It's a demand. And a punishment means that you don't get to say no (well, within the confines of the relationship anyway. You can of course say "no" and leave the relationship, but it's fairly doubtful that a Dominant will keep a submissive who refuses to be punished). And that's also unacceptable.
If you were more open to the idea of anal, and the punishment was to consist of something other than anal and then anal afterwords (i.e. a kind of "redemption" involved in the punishment and a restoration of being pleasing to your Dominant) then that would be different.
Maybe. I'm very, very hesitant whenever someone adds an explicitly sexual act (such as intercourse) onto a punishment and even more hesitant when said person intends to use said explicit sexual act as the entirety of the punishment. If you wanted to explore anal with your partner becasue he wants it and you are okay with trying it because you want to please him, then that's fine. But if he's demanding it for some perceived infraction despite the fact that you are scared and do not want it, then that's most certainly not. Have you told your partner about your fears relating to anal? If not, then now is most certainly the time to do so. He might even change his mind about the punishment he wants to give you. If he does know, then I'd honestly advise against pursuing a relationship with him. If he intends to punish you with a sexual act that you do not want, that could mean that he intends to "break your spirit" (or "break you in") with this punishment, and to do so against your will. And again, I find that to be utterly repulsive and unacceptable.
If you want an alternative suggestion, that post Callalily quoted gives a decent amount of advice. If you want a more 24/7 perspective (as I'm not really sure what kind of a relationship you are getting into) my submissive and I actually did a joint response to the last thread Callalily began here
http://www.psychforums.com/bdsm/topic168141.html where I talked a little about separating sensation play (or normal play) from punishment without crossing limits. It's a bit of a long read (as I'm rather verbose) but I think it's a pretty good explanation for how things should be done and will shed further light on why I'm so opposed to what your Dominant is intending to do to you.
And Callalily, with all due respect I think you're a little off-base here. First of all deeming BDSM as a whole problematic due to the fact that submissives find it difficult to say "no" to their Dominants on certain things is misguided. Even though I completely agree with your assertion that it's difficult for submissives to communicate with their Dominant's in general (as I've experienced this to what used to be a frustratingly common degree with my own submissive) I fail to see how this is a systemic problem as opposed to an individual problem. For instance, most of the things you reference in your examples are conclusions that the submissive in question (hypothetical or real, I do not want to falsely-attribute those thoughts to you) deduces without talking to their partner. For example, when the submissive in question comes to the conclusion that he or she must be like the "pain sluts" on the internet, he or she does not discuss this with his or her Dominant and determine what he or she wants. The problem here seems to be that the submissive individual is unwilling to communicate with their partner, as opposed to the idea that BDSM is oppressive (and thus problematic)in any meaningful or quantifiable way. While BDSM may be a
contributor to the situation, I fail to see how it is the
cause here. In fact, I suspect that this individual would likely have difficulties communicating with most partners as the feeling of "I need to say yes because I am submitting to this person" would be replaced by other justifications such as "I don't want to impose on this person, I should just keep quiet" or "It's not so bad, I can live with this", etc. This is the definition of a
personal problem and as callous as it sounds, it's this individual's job to resolve this issue. This issue is also why I stress communication so frequently to other Dominants and submissives: If your partner doesn't know there's an issue then they absolutely can do nothing to resolve it. So, while I would agree with the general claim that this is a problem I find it less a problem with the system than with the individual in question. And the fix? Communication and education of course.
Second, I think I've talked about this with you before but I entirely disagree with you on the notion that Dominants are not selfish. I am very, very selfish. My pleasure matters more to me than my submissive's pleasure. That's the definition of selfish, right? However, my submissive's
welfare, and well-being are also of paramount importance. Because I love her, and it lowers my pleasure when she is doing poorly, is upset, or is having difficulties. Additionally, if my submissive is upset she is less able to please me up to my expectations. Therefore, in order to derive the greatest possible pleasure from my submissive I often do things like cheer her up, talk her through her problems and empathize, etc. Not only because I want to do them (again, the whole "I love her" thing comes to mind here) but also because she will be more able to please me
due to these things. It also pleases me immensely when I make my submissive orgasm. In fact, I think it might please me about as much as it does her. So I tend to do it. Quite a lot. See? Completely selfish. Now if I could only convince my submissive of that

. Because she agrees with you. Completely. But I do agree that reactions are very important.
And ouch! Next you're going to tell me that all women don't secretly want to be tied up!

But in all seriousness, most people start off by saying that they don't want to do anal, and that it's a hard limit (my submissive started off saying the same thing) and quite a few of those (not the majority by any means but a significant minority) do end up amending that. So, I think the issue is less that he thinks "all women secretly want anal" and more an experiential issue where all women he's dated or talked to initially said they didn't want anal but turned out being fine with it. It's less a problem of stereotyping and more a problem with egocentrism. But, I might be giving too much benefit of the doubt here. I tend to do that sometimes.
Best of luck and best wishes to all involved, and special thoughts to SubinDoubt and hopes that this situation is resolved quickly and satisfyingly,
-MJH