This is the same fallacious reasoning people use to advocate many laws, drug prohibition a popular one. For instance people will say if drugs are legal then it opens the door to people being intoxicated while driving or harming someone else in x other way. But of course these are already illegal in of their own.

What you’re looking for here is protections of the elderly against abuse via coercion to act counter to their best wishes. This is a separate concern that needs to have laws and parameters around it.

Virtually anything can be “an opportunity for abuse.” Look at the internet. That’s not a good reason at all to prevent it, it’s a reason to outlaw and protect against the abuse.