BDSM is by its nature/activities in most countries is illegal, both in activity and photo/video representation. Sure there are some weird, historical legacy laws floating around out there covering activity that is not BDSM, and in most (not all) minds is fairly vanilla but regarding much BDSM activity its illegal.
If you have taken alcohol, or any drugs that are legal, that alter the ability to think clearly you can not give consent to anything.
Impact play - anything that leaves marks on the body, regardless of what toy did it is considered to be assault. One can not consent to assault. In the UK, anything that leaves marks that are not 'trifling and transitory' is assault and illegal.
Breath play, choking - assault, attempted homicide.
Bondage - could fall under various laws related to Imprisonment. In video/photo representation if there is no obvious way to remove consent, its illegal, as is all four limbs being restrained. So spread eagled, gagged and blind folded in photos/videos, that in the UK is illegal.
Rough Sex - could easily fall under sexual assault laws and if CNC, that's rape, the law does not recognise consent no consent.
D/s/M/s/1950s/taken in hand, fin dom activity/dynamics could, at its core, excluding any actual activity, fall under coercive control laws. Does the law recognise giving consent for what is a controlling relationship, with punishments. I think not. In essence one can not renounce ones human rights, only the state can do that if you are found guilty of a crime.
I could go on, but obviously different regions will have some variations on what is and isn't legal. However to say nothing illegal in ones profile, essentially boils down to no BDSM activity if one wants to stay strictly within the law. That is why, in my opinion, its a ridiculous thing to say.
Taking drugs (not illegal everywhere), bestiality (not illegal everywhere - yuck) prostitution (not illegal everywhere) for example are not in and of themselves BDSM activities, though they could be included. Sure list them specifically, but not under BDSM activity, and regarding BDSM its not legal pretty much anywhere, though a few places are a little bit more open to it being part of peoples lives, such as in Germany, and the Nordic Countries. However some of these activities can fall under general laws regarding assault etc.
https://en.wikipedia.org/wiki/Legality_of_BDSM