In my experience, it's easier to ruin wine than beer. Wine is more susceptible to problems, simply because it's in the fermenter longer. Headspace is a problem, and sometimes people don't realize that and they get mold or infection just from allowing the contact with air. Or aceterobacter from fruit flies- a huge problem for me in the summer. As was previously mentioned, wine isn't boiled like wort for beer, and that is yet another avenue of potential infection.
Sanitation is critical, and so is siphoning properly. I use campden tablets to minimize oxidation risks, but with beer it's consumed relatively quickly so I don't worry too much about oxidation with my beer like I do with wine.
Wine is easier to make, but easier to ruin. In my humble opinion.
Kits are which are pre-sanitized and quick to bottle, so probably not as much as a risk in making them. In grape wines, you've got acid adjustments, pressing, etc, which can also be problematic.