I think you're generally right: RT4TJ arguments are often baseless, as the "right tool" tends to be what you have available in terms of extant code, dev tech, and people.

However, just because the argument is often misused by people who don't understand it doesn't mean it is without basis. For example, Perl is not the Right Tool when performance is King (say, 3-D model rendering and shading). Neither is Java, for that matter. You'd probably use C or ASM for something like that.

I think the fallacy comes when people start to think that for any given application there is One True Language that is the Right Tool for that job. The Right Tool argument really has more to do with narrowing the field, not the ultimate choice.

Except in those cases, the choice is less about the nature of the problem/solution, and much more about the specific constraints of the specific situation outside the problem (i.e. what resources do you have, and what work can you borrow to make your life easier).