Ancestry.com does allow the display of living persons and the birthdates. I have had to ask people to remove it from their online databases. Ancestry.com will not even if you can't get a hold of the submitter. Submitters apparently have the option to display or not display living person data that is uploaded. Legally right or wrong, it makes us all more vulnerable to identity theft.

Synching to me means you want to keep the data the both the same offline as online which would mean living person information. In addition to the personal id information (name, birthdate, mother's maiden name)FTM users sometimes collect other sensitive facts and write notes that should not be on a public site.

When you upload a Gedcom, it states:

By submitting your GEDCOM file to Ancestry.com, you agree to the following:
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Ancestry may reproduce, compile, and distribute, all information about non-living individuals in your submitted GEDCOM file.

Ancestry will make reasonable efforts to hide all information about living individuals (except the surname) prior to reproducing, compiling, and distributing your submitted GEDCOM file. If a date of death is not included on any particular record, we will use a process which in our belief excludes the living.
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I have a couple problems with this agreement. One is that you are turning the rights over to Ancestry.com to distribute your data..no matter what the validity of the data. They have sold CD's of family data before from those who have submitted data to Ancestry.com!

The second problem is that they will make a "reasonable" effort to hide all information of a living person. Between making a "reasonable" effort and allowing submitters to choose the option to display living person information, it doesn't seem good to have living person data flowing back and forth through their system.