If these same sex couples come in the restaurant and do their kissing, is there a law that allows the manager to have cops remove them? It would be the same with heterosexual couples doing that. I wonder where the line is that it becomes lewd behavior in public.
It's all in the intent. A stranger can be innocently touched, and it can be safely assumed to be an innocuous gesture when both parties are reasonable and context-aware. The exact same touch can be assault when it is reasonable understood to be unwanted and the intent of the assaulter was to inflict discomfort, embarrassment or any other malevolent purpose.
These "kiss-ins" are the extreme perversion of the purpose of a kiss, to express love and affection to the close one you love. To turn this good gesture into a political statement is pernicious to the extreme. And to aim the display of it at others as an act of harassment can be considered a crime - "disorderly conduct" in Texas.