In that situation I still tip, just less, since my "load" on the restaurant staff is much less, no one had to take me to a table, take my order, bring my order, and clean my table. The tip is for the kitchen and for boxing/bagging up my order in that case, essentially.
I hate that even that is required, though. I would gladly pay an extra 15-20% for the food itself if I didn't have to leave a tip & the staff was paid the "normal" minimum wage, or more.
Yea, I always figured tipping was paying for table service, but who knows. Ambiguity around what it's for and how much is "normal" is just one of the many, many reasons tipping is so idiotic.
No one likes tipping, but it's become a moral issue. Something transformative has to happen in America to change the situation.