If you really want less seats, then just pretend they're not there. Image the seats were demolished and the cost of demolition was offset exactly by sale of the salvaged materials (which is actually quite a good deal). If you happen to fill thoses imaginary seats, just send me the extra revenue.
Seriously though, I think not having the option to remove seats is reasonable. Demolishing part of a stadium surely cost more than sale of the salvaged materials, so why even make this an option? Also, I don't think the 'soft cap' is an issue, because even if you have 'too many' of one type of seating, it does not affect the occupancy of other types of seats -- at least I am pretty sure this is the case.