You're right - I did not pay for the seat in the first instance...but my point is more that I chose SK based on it's offering at the time which was seat selection being possible for free...
if it had not been free when I came to purchase the flight I may well have selected a competitor.
Now they've got my booking, they've changed their mind and introduced a policy requiring further payment to select a seat...surely that should only apply to bookings made after the change in policy.