I would assume two things: walking a few steps behind is one thing; doing it with a collar and leash in ordinary public places (outside of the types of clubs where this is generally considered norm for this venue); therefore there is an exhibitionist component as well as the BDSM dynamic.
I would also assume that they are very inexperienced and new to this lifestyle.
I know a few experienced people involved in this and the basic motto for the lifestyle as a whole is: safe, sane, and consensual.
People with maturity in the BDSM scene are very very discreet and they wholeheartedly adhere to the three principles just cited.
They definitely don’t go parading it before the general public in ordinary everyday places. Why, you ask? Because while this is obviously consensual between the two of them, the rest of the public has not consented to be the voyeurs so this couple can get off on their exhibitionism.
That amounts to involving everyone who sees them without their consent.
If they’re doing this at a club or an event where this is de rigeuer, then everyone going to that club knows the score and has given their “consent” simply by their attendance.
But nobody in the general public present at the mall or hotel lobby was expecting to be yanked into this couple’s BDSM dynamic.
Involving others in your “scene” without their consent is just considered bad manners. Find another way to get your jollies.
Suppose there were parents with children staring open mouthed?
People who are into these kinky type activities are marginalized enough by a society which has no understanding of why people choose this. Why give them more ammunition?
So, no I don’t think they should be banned but I definitely feel that they could use an iota of common sense and discretionand keep their private sex life private. These folks are a half step away from the flasher who gets his kicks through exhibitionism. These folks are also exhibitionists and I don’t blame people looking at them for being judgemental. No one wants to be going along doing their shopping at the mall and being accosted by these dimwit.