Yes, as far as I can see it does decrease the overall quality of answers, however, having more answers is - from my perspective - beneficial, even if some of those are low-quality.
Please note that I - in this case - do not classify VLQ questions or non-helpful questions as low-quality. Low-quality is something that I'd understand as "Do X", without giving any explanation (i.e. of why X is required), terrible formatting (to the point where the readability is heavily impacted) as well as partial answers.
Giving an answer, even if low-quality and/or partial, can help the user who posted the question. It can also serve as incentive for other users to post an answer, based on the low-quality one but better (added explanation, more in-depth etc.) or to edit the existing answer into shape.
It does naturally decrease the overall quality, but also lays the foundation for the ultimate goal of any Q&A site, which is having every question, and a fitting answer.
In conclusion I'd say that the "proper" way of dealing with this would be the following:
If a question has a low-quality answer, one should either improve that answer by editing, or, if the edit is too significant, post a new answer, and downvote the low-quality answer.
Many people nowadays seem to underrate the moderation tools given to us, and downvotes are one of those.
The encouragement to add an answer is helpful, at least in my opinion. The community will be the judge of whether it'll stay or go.
