Does binge reading manga ruin it?

Like above, if it's finished publishing, then the best way to enjoy a manga is to binge it (ie. read it all the way through without long breaks). I've noticed in many chapter discussion threads, particularly for manga published monthly or longer, the early commenters who are reading chapters as they're released are often frustrated and annoyed by pace. The latter commenters, on the other hand, who have started reading the manga after completion or at least have several chapters to read through at their own leisure, are much more invested. Manga (and anything, really) reads a lot better without pauses. It's easy to forget context, details, character, etc. In many of the Berserk threads, when there would be only a couple of chapters a year, so many commenters lose their patience with the pace and trickle of content. It's understandable; all these breaks slowly pull you out of the series. The latter commenters who don't have to deal with months of waiting are totally different in tone and overall much more agreeable. It's why I typically don't follow monthly manga anymore.

I don't think so, as long as you don't force yourself to read as many chapters at once as it's possible. It's mostly the case with series that are already finished, or are ongoing, but with a lot of chapters.

Where it might be a serious issue, though? I think mostly when it comes to mangas that have irregular release schedule, like Berserk. After binging almost 400 chapters someone might feel down to see, let's say, few chapters (circa 20 pages long each) released per year.

Oh, that kind of breaks are no big deal, to be fair. On the other, hiatuses lasting for a long time, counted in years, like in Saint Seiya: Next Dimension's case... now they can be problematic for viewers, since in many cases - which is normal - they need to remember what was happening in the chapters prior the hiatus' start.