It's obviously not exactly the same as stealing, since you are only denying the person one very specific use of their "property" (which only recently has been artificially made property, through copyright laws). That specific use you are denying them is not the right of sale even, but the right of a monopoly on distribution. Of course, if it starts materially affecting the person's capacity to live a reasonable lifestyle, then it becomes a different moral issue, and there is still a moral judgment to be made regardless, but that is not the same thing at all as conflating unauthorized copying, which widens possession in a way that could potentially have averse effects, and the absolute of theft, which changes it in a zero sum way, and necessarily has averse effects.
As one example, I know a guy who pays for online streaming subscriptions, but still pirates to not be forced through a crappy experience because people are attempting to extract the last penny and get as rich as possible through spying and ads, tiers of resolution, device restrictions, etc. I see no reason why there is any moral issue with bypassing their chosen distribution monopoly, especially because they are not starving. I strongly disagree with the tenet that extreme capitalistic gain is a right, and thus cannot consider intellectual property rights as such an absolute. Now, if one is to download something that someone earning a modest living made, and which has a real material impact on them providing for a reasonably comfortable life for themselves and their family, personally I consider that a problem, but that is quite rare (not least of all because smaller content producers are usually being exploited and making very little from distribution). It's not the likely case even with just a modicum of awareness in what and when you decide to download something.
