Say I am a bit lazy and use the heavily downvoted suggestion
Why would you go and use the advice in a downvoted suggestion? When it is greyed out and there is an answer with upvotes just above it? When the comments make it clear people think it is stupid advice?
That's not lazy. That's going beyond reason. And frankly, if someone goes ahead and does that, they deserve all the pain they get.
What you are suggesting could happen is not reasonable in my eyes. That it may have happened once or twice doesn't make it a big problem.
Wouldn't it make sense to delete that unhelpful answer?
Sure. Vote to delete it then.
But - just deleting highly downvoted content automatically on the network meta doesn't make sense to me either, as the function of the site is also for discussions - some opinions may not be popular but they should still be seen and be around.
Point being - this needs to be done case-by-case.