This is a good question and one which I asked a few years ago I think. There are many angles to this one. Firstly, as I have said on many occasions, the internet is an absolute magnet for certain types of personality flaws. People who desire attention will always make up a whole bunch of cr@p to gain what they crave. If it is part of a compulsive illness they will have no choice in the matter either which is most irritating indeed. There are many who like to get one over on other people to give themselves a sense of achievement, i.e. the deceivers. They gain a cheap thrill by making people believe what they are saying even if it is total b/s. The power rush from this is pathetic and you just feel sorry for them. Imagine how pathetic an individual must be to have to deceive people to give themselves a feeling of power or authority somehow or other. There are also many anti religious people who, again, get a sense of achievement from leading as many as possible away from their beliefs like a gunslinger cutting notches in a gun belt. We know there has been an absolute explosion of fake news on the internet. A lot of this is for psychological gratification as stated but there are also, obviously, those who know that large scale attention can prove lucrative financially. So really the internet and particularly sites like this are irresistible to those who are wilfully arrogant and like to exert themselves over others or simply command their attention. Even reading through some of their questions will give them an enormous sense of gratification and the more people who respond, the more of a thrill they will get.
I agree that when a genuine case comes up of someone feeling desperate there will be many who have seen it so many times that they will assume it is yet another troll and give an answer which is actually very unhelpful or even rude to the person who asked the question.
Often the most difficult to deal with are the anti religious fruitcakes who like to pretend they are believers. Part of the reason they do this is to prove to themselves that if there is any truth in what believers say, they should be able to see through them, i.e. if they are being righteously guided. The reason this is so difficult is that if these people are amongst those who reject religion completely, they are therefore amongst those who, ironically, don't deserve any sort of proof whatsoever. This is a tricky concept to grasp but the end result is that believers are only required to speak the truth and they will gain reward by so doing but there the obligation ends. Those who reject faith do so by their own free will and as they say, you lead the horse to the water but if they refuse it is down to them. Even Jesus met people who rejected faith and His example is that there is little, if anything, which can be done for such people.
Lying and deceiving are becoming part of our culture, as is pointed out in the scriptures. All you can do is to answer in good faith and adopt the attitude that if you have given a good answer then maybe someone who is better deserving of it will see it regardless of the jerk playing games. I hope that helps.
As to whether yahoo should do something about it this is a difficult one as you get into the grounds of impinging on an individual's right to free speech, i.e shutting the person down could be construed as censorship I guess.