The alternative to it being a “slippery slope” is that it becomes an unused and unloved feature. We should want new syntax to influence the way people code, otherwise why are we going through the rigmarole of changing the language.
The match statement was added specifically to help guide users away from runtime type checks and towards structural matching. (Whether it’s achieved that yet is irrelevant.)
If you don’t care about your syntax proposal having an effect on how people code, then just say so, but I expect people will take the proposal less seriously in that case.
Alternatively, if you think it’ll have a different effect on how people will code (a different “slippery slope”, if you will), then describe it and convince people it’s a good idea.
A proposal to add syntax just for the sake of syntax is going to find opposition from all sorts of directions. The best example of that is this actual proposal in its various attempts over the years.