Because Kira was right there with them blowing stuff up and sometimes killing civilians in the name of a free Bajor and the Prophets... hey wait a minute!
I can't tell from this comment, but yes, I'm doing a rewatch rn, and Kira very much admits that she killed non-combatant cardassians during the occupation, and much of the first season is her anger at what the cardassians forced them to do.
Its made very clear later in the series that Kira considered civilian targets acceptable. Paraphrased from her own words "If you aren't with the resistance you are with the occupation."
DS9 could have never gotten away with its nuanced portrayal of the terrorism/freedom fighter debate post 9/11, but its more relevant today then it ever has been.
Sorry, I interpreted your first comment for some reason as saying that Kira did not target civilians and blow stuff up, and so she wouldn't be considered a terrorist by today's standards. Yes I 100% agree she would, and she would be demonized as much as the Palestinian resistance is today.