Actually your SIL was alot more tactful than I would have been if in her position. Altering a child in any way doesn't sit right with me, including ear piercing etc.
I think you are a huge hypocrite OP - FGM disgusts you but you are willing to do the equivalent to your son? FGM is done in alot of countries in the name of religion, removing a piece of anyones body against thier will is disgusting. Why not let him have the choice himself when he is old enough to make that decision?
There is an alternative ceremony you could have, the brit shalom.
Primafacie I probably know more circumcised men -Jewish, Turkish, Asians, Canadians, Americans- than all the "it's child abuse" brigade put together, and if you asked any of them whether they are traumatised or have less sexual satisfaction as a result of circumcision, the answer would be 100% NO. Randomised studies have produced the same outcome, so yes, there is actual data on the point.
Your point here is totally null and void. The vast majority of men who are circumcised in adulthood who have already experience sex with an intact penis report that a few years after the circumcision they lose most of the pleasure during sex as the exposed skin becomes toughened over time, this effect is even more pronounced in men who were circ'ed as babies. Quite frankly men who were circumcised as babies/children don't know what they are missing and would probably feel robbed if they did. There are countless men upset by thier circumcisions, go look online into the many support forums set up for these men who are very angry that this was done to them without consent, some even opt for foreskin reconstruction.
Quotes by men describing sex after adult circumcision:
Like sight without color
An orgasm for a circumcised man is similar to "each stroke" for an intact man
An orgasm for an intact man is 'incomparable to anything a circumcised man will ever experience.
And there are studies which prove this, this page has a link to the full article.
www.nocirc.org/touch-test/touchtest.php
Most of the 'benefits' in the link you supplied are not risks at all if the man practices safe sex (and plenty of studies disprove these 'benefits' anyway), the cleanliness 'benefit' has been disproved, the too tight foreskin in teens/adults is rare and can be resolved in other ways or as a last resort, circumcision in adulthood when the person can make the choice themselves, and penile skin cancer is even more rare. All so rare that it is not worth the health risk of circumcision in a baby. You do realise that some babies still die from circumcision don't you, circumcisions that are performed in hospitals, in a sterile environment by experienced doctors.