Now, in each of these cases, well intentioned community members edited those posts, removing the spam link. Problem solved right? The answers, which 'provide useful content' (as per voting, I make no claims about the quality of these answers) stay, and the bad links go bye bye.
NO. Problem not solved. Y'see, when those edited answers stick around, our spammer friend is able to accrue reputation. And eventually, with rep, come a variety of privileges that will allow him to place his spam in ever more harmful places. Places that are supposed to be protected from unhelpful and untrustworthy users who do things like post dubious links to bad places. The only way to prevent spammers from earning reputation, is to ensure that their posts are swiftly flagged and deleted, and, since we're talking about spam flags here, their account rapidly shut down and prevented from further vandalism of our little corner of the internet. By editing these posts, the spam is hidden, and the flags don't get cast, and the spammer gains rep.
So please, in the future, when you see spam buried in an 'otherwise good' answer, JUST FLAG IT. Trying to salvage the content only risks creating more problems down the road. If the answer was so brilliant that you feel it truly makes the internet a better place and belongs on the site, repost it yourself. If you feel guilty about taking a spammers rep, I have two things to say to you:
1) Never feel guilty about taking reputation away from the sort of soulless monsters that are defacing this community.
2) If you still feel guilty anyway, switch to a private browsing mode in the browser of your choice, and post it anonymously.