Should songs only ever be allowed in the charts once?

After Westlife ruined Home, a brilliant song by Michael Buble and got to number one (they do this a lot!) I would love for covers to be banned. They are rarely any good, in fact u nearly always hear 'its not as good as the original' Sugababes/Girls Aloud murdering Aerosmith/Run Dmc Walk this way also springs to mind recently And i dont care that it was for charity, it was still shocking! Plus all the good songs from 80s, that have just had a new beat put behind them, then the rereleased as new songs. A lot of people dont know DJ Sammys Heaven was a hit for Bryan Adams. Why cant 'artists' be forced to write their own material, I'm sure Westlife and the like would not have half as many number ones if this was the case. What do people think on this? Should artists have to write their own songs? What is gained from covers of songs being released (apart from the obvious fact that it makes whoever owns the rights plenty of money...)