People and their views can change over time and some people also tend to do stupid things in their youth (just have a look at some Facebook profiles). I think if the internet has archived something disadvantageous that could affect that person's life, it shouldn't be a big deal to remove it or alter it in a way that it doesn't cause issues (if technically possible). We're all human!

For example imagine you heavily criticize React and the way Facebook is handling their license, you even may get emotional while doing so. This may not always come beneficial if you decide to apply for a job at Facebook some day. Mistakes happen and you, as the "Online Reputation Manager", can help to resolve these with a few clicks. Doesn't sound like a big deal to me. :-)

I don't know what this was about, but if it was something that really could harm that person, then I definitely would have altered the comment so that it doesn't affect that person's life. With that said, I think in that case you've done the right thing. On the other hand, I definitely would refuse to delete / alter comments if there are not such issues.