I do dislike spamming post etc.
It's a waste of time. (still it improve our logic to read past thing that isn't worth it (maybe this post for some people), can be useful outside the virtual world, let's take what we can out of it)
But let's look at the "other" side, if someone has taken time to do such a bot, it has to be lucrative in some sort. Otherwise they will stop running them if their cost is too high and do something else to get what they want.
To my eyes, it's the same principle as to those who fall the "XYZ prince that will give you millions if that unlucky prince can't get out of his country by having a few buck from you". Only need a few that "believe" in that story to make their profit. From the mass, some will click... and I'm pretty sure they measure that.
The web help lowering the "running" cost.
Before they had to pay for the paper, ink and sometimes a stamp / or someone to carry the letter.
Let make it enough difficult (captcha for instance) to make it worthless to those you does it.