It befuddles me that anyone would object.
First of all, while somebody might remember there relatives anniversary date there should be no assumption/expectation that they do or will.
Second, you figure that in general most people want to wed on a Saturday. It is obviously OK to choose a different date but to avoid work conflicst, allow travel time, etc. Saturday seems to be the only option that makes sense for a lot of couples.
Third, holidays seem to eliminate some of those weekends for a lot of people. They might not want to get married the night before Easter for example, because it could create a onfolict for many guests.
Fourth, a lot of couples wouldn't mind at the shared dates at all. I think my siblings and their spouses would probably see it as "Hey honey, we will be able to go out and have an evening out, go dancing, etc. on our anniversary - on somebody else's dime."