While implementing rebellion we discussed with
@lottendill and
@SadShogun (who implemented that feature) this (players to capture rebel towns) will be the common case in future. I think its good to have this because otherwise player need to attack kingdoms which are generally stronger than rebels to take their initial fiefs which can cause problems for them, when player take a fief from a kingdom kingdoms come back with strong armies to take it back. So rebellions are good for players especially starting their kingdoms to get a new property without being enemy to kingdoms. When you do this you do not be enemy to old owner of that town but actually that kingdom lose a town to player. Maybe player can lose relation with king of old kingdom in this scenario but this case is not enough for starting a war.
Also in another post one player mentioned he want to recruit rebel clans which lost their initial town and waiting in a castle player owned. I think this can be a good feature too. We need to think this.
About security to effect tax income, I dont like we have a direct 10% penalty when security is lower than 25%, its already very low effect and make things directly effecting each other, already security effects loyality and loyality effects tax, I think having a third direct effect : security effect tax is much. I prefer an indirect effect of security on tax something like
@Earth Dragon suggested. Only loyality should be direct effect on tax imo.