[Suicide Junkie]

It adds.

I also noticed that SE4 dosen't complain about NEGATIVE values for boarding defense ability...

You might be able to make crew quarters easier to capture, or have specific components cause a ship to be easier to capture.

EG: Kamikaze Self-destruct device. Reduces boarding defense by 100 points. That encourages enemy ships to attempt captures, and then blows them up!

If the KSDD gets destroyed, then your crew & security stations will be able to prevent capture normally.