Not sure if this was already discussed, but I am confused about the use of -ing form/infinitives as complements. I've found in several threads in Stack Exchange that the verb "to be" has to be followed with an infinitive form like in the example:
What we want is to be free.
All you can do is (to) wait for the results.
However, I've found on other resource that verbs in their -ing form are used as complements too, like in this sentence:
The group’s main goal is eliminating poverty.
Even Practical English Usage by Michael Swan states that -ing forms can be used as complements (like: "My favorite activity is reading poetry").
Then I am wondering if the below sentences can be considered correct:
What we want is being free.
All you can do is waiting for the results.
If the above examples are ungrammatical, may I know the reason?