To foreign key or not to foreign key

I know this has been discussed here before and i did find a couple of jonathan lewis's old posts  

The thing is we have a project where the consultants want to ensure about 10-15 foreign keys per tables to enforce parent child relationships. I've seen locking issues beforer and was wondering if the list could put down a some pros and cons as to going or not going with a primary foriegn key strategy. This is a oltp type system and sub second response is what the enpd product requires( isnt that the description of every project these days). The consultants want every foreign key indexed. which i think is way too much a performance degradation since inserts are going to be major part of the application.  

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