Kevin, I am not aware of anyone claiming Bloody Sunday was self defence.
I am surprised you thought it helpful to open that can of worms.

When Israel removed its troops and settlers from Gaza, the rain of missiles began.
Would you deny them the right to take action to reduce the attacks on their citizens?
How is it not self defence, provided it is not indiscriminate or disproportionate?
How is launching a missile loaded with ball bearings indiscriminately at a town self defence?