> It should not be an Error if a user wants to include both PanX and PanY as separate tools in the same plot?

Interesting question, but not necessarily it is an error... maybe a user wants to have specifically panx and panys tools, because it makes easier to interpret his/her plot... 

> Ah And Damian mentioned about "throwing a warning".

Yes, I see "throwing a warning", because I thought it would be enough, but reading the @bryevdv answer, I think an exception is better...