Having tried a few merges without being on the trusted list for all of the extended family members (and therefore having to be a nag to the profile manager to get the doubled children merged), I would support this. BUT, having worked for a decade or so trying to untangle the myriad "same name" ancestors of 200 and 300 years back, I shudder to think of the chaos that someone could cause doing merges just in my tree! So, I wouldn't support this. For example, there are six profiles with the name of one of my ancestors (born in the 1600s) that are nearly identical - but none of them are actual matches. They're mostly cousins (within 40 years, you can have a Sr., Jr., and then a different set of Sr., Jr. when the original Sr. dies, and most of the sons name sons for their father and brothers).
However - is there maybe another level that could be applied for Open profiles... maybe an "open trusted" level that doesn't allow merging? (Not sure how to address the "cleanup" merge issue, of combining the children/spouses of a merge; maybe adding a bulk trusted option [in addition to all descendants, all ancestors] of all ancestors and one generation of descendants and their siblings?)
Maybe a simpler option, although still with potential pitfalls, would be that only the profile manager can delete a Rejected match, and no one but the profile manager can initiate a merge if the match has been rejected (actually, that's current, right? - a merge can't be done if that match has been rejected? - so it would only need the piece that only the profile manager can override/cancel a rejected match...might get the added benefit of more people searching for matches and "pruning" the tree a bit :)
Sorry for the long answer, but it's an interesting question, with really significant pros and cons.