But, for exposition: It mainly comes down to your intentions.

1) NoScript is tampering with how a website is presented. If that includes tampering with their ads, then possibly. Definitely so if you're using it for that purpose, like adblockers.

2) If you're using a client that cannot support javascript because that is all that's available to you or all that you are able to use, that might be considered fair but actively doing so to skirt advertisements would be stealing.

3) Not everything will work in every browser, and sure you can take advantage of that. This isn't stealing, it's just how compatibility works. Tying back to the other points, there are sites that use text-only messages as advertisements to still show up for people without javascript/using text-only. Some publishers don't feel this is worth it. That's for them to decide.

Yes it might sound subjective but this is no different than going to a store and taking stuff... only there they can stop you before you take it. The internet by its nature is open and accessible, meaning there are very little controls to selectively stop people. For example: there's no easy way for a website to block NoScript users so they have no control. But just because they can stop you doesn't make it right.