http://www.vancouversun.com/travel/Birth+tourism+rise+Vancouver+Richmond/10713600/story.html
Let's just say I've also 'heard' how easy it is to do and how many are wanting to do it and leave it at that when it comes to numbers. Right now, it's a small aspect. But the challenge is in the fact it's a growing problem, unless you curb it, it only continues to grow and then becomes a tough industry to stop, especially at the home country where it becomes a viable business.
Canada doesn't have it so bad. Most Americans would rather give birth in the US, and we have no large land border with Mexico or another country where it's easy to cross and enter.
But it's not really such a shake up to our values or constitution. Most European countries are far more tolerant and accepting than us, and they still don't allow birthright citizenship unless one or more parents are citizens at the time of birth. It's very easy to curb this, but the political will must be there too. Obviously you'd take into account permanent residents and foreign nationals working and residing in the country. But how people, just visiting the country, giving birth and then getting forever citizenship and the benefits to go along with it, should be allowed or condoned, I don't know.
Unlike other people, these people have no intention of staying or living or contributing to the country either. Many leave and go back and then use the citizenship when it's convenient (ie. Purchasing real estate, needing consular or embassy services, emergency medical help).