Allo!  Curious:  If I were to create a product for resale using made
up (but wholesome and positive) quotes from different celebrities,
would this be illegal?  Like (clearly this is just a lame example)
"Math is my favorite subject in school, too!" in the first person as a
satire from a celebrity.  Can people take legal action over nice,
benign things being said as them?  I have an idea that I'd like to
make some money off but don't wanna do anything to get in trouble.

I am not a lawyer.  Having said that, I believe you can make fun of
anyone you want to without having to worry about legitimate legal
action (although anyone can sue for anything).  Satire is protected,
as I understand it.

No, even if you quote them as saying "nice" things you cannot
attribute words that they did not say to help you sell a product.  If
you could do that what good would their real quotes be worth and who
could tell the difference?  It is also fraud.

You cannot attribute quotes to a celebrity if a reasonable person
would believe that the quotes were real.  If it is clearly and
obviously a satire then you would be ok, but not if it "seemed"
legitimate.  For examples, Saturday Night Live does sketches all the
time where they have the "president" making speeches, but any
reasonable person knows that this is fake and they are protected.  On
the other hand, a movie studio was recently caught making up quotes
from movie critics praising a movie that were fake and they were in
serious legal trouble because they made them out to be real.