It depends on when your walkthrough occurs, whether they have an exit path, and whether the user feels like they got any benefit from it.
If the walkthrough occurs early in the process of using your service, you're increasing the likelihood that they'll give up entirely on your service and move on. People want to try things out, they don't want to have to spend time learning about what they're about to try out. A walkthrough is even more annoying if it is truly forced with no exit. If you don't give people an exit, they've always got the exit of not using your service at all.
If the walkthrough occurs after they've been using the service for some amount of time -- that is, they've had time to try it out a bit and get a feel for what it does and how it might meet their needs -- then you're less likely to raise their ire, and you're also more likely to be able to give them information that helps them use your service until you fix the endemic UX issues that you have that makes you need such a walkthrough in the first place. Even in this case, forcing them to sit through it with no exit means that you're eroding their trust.
As someone providing a service, you have to build trust with those who are using your service. They need to trust that it will meet their needs and that it will allow them to do something that they weren't able to do before (or will allow them to do something that they could do before, but now they can do it better/faster/cheaper/whatever). By forcing them to do anything, you're taking away the trust that your service will meet their needs. You're telling them that you know better than they do, which is very rarely a message that is taken well by people.
Remember, "it will benefit them in the end" is from your perspective as the provider of the service. However, the people who are trying to use your service don't know that there is benefit to be had, and they do know that you're treating them badly by giving them a bad user experience and, on top of that, forcing them to sit through a walkthrough that they don't feel that they should care about.