Incest

Because "incest" isn't a noun which forms a plural, nor do plural nouns take an apostrophe.

Because they can cause a lot of damage to farmer's crops.

Locust are a good example of this.

Some times you just bug the hell out of me, Lordy.

I used to like to light a few sticks and then enjoy the aromatic smoke flowing through the rooms, especially Jasmine, but my doctor told me to stop because the fumes might hurt my lungs.

Joe(that made frankincense to me)Nation

Hi,Thank you very much for that. I come from an Asian country, I am not well with speaking and writing the English language . I meant to say that,why is incestual relationship deemed as wrong?Forgive me for my bad grammar.

We all know what you meant !
Incest has been discussed on this forum several times. It has biological, social and religious aspects, so the word "wrong" can be examined from any of these points of view. A range of answers can ensue from "acceptable" (as in Ancient Egypt) to "unacceptable" as in Christian culture. You should note too that the definition of "incest" has been prone to manipulation by third parties, such as the Church, in order to acquire estates from the nobility which tended to marry cousins in order to maintain continuity of wealth.
However uou should note too that most people who ask your question have an interest in the possibility of an incestuous relationship of their own

If it is not wrong, then why is it illegal in the vast majority of countries around the world?

The dangers of inbreeding, perhaps?

Making something "illegal" does not mean it is right or wrong. It merely means that it is against the law. How many laws have been changed over the years ? Does that mean that because the law was changed the "legal" is now right? Not defending incest here but bringing up a point that right or wrong is not determined in the courts.

I agree. Each country is different with regards to relation and age. In short, it is what is acceptable in the country of origin. As they say, when in Rome. I will say though that biologically there is a problem if it turns into having a baby.

Have you actually done any research at all into the dangers of defects brought about by inbreeding?

The incest laws in place around the world are primarily there for very good medical reasons.