There is if it's overused or lazily used. Nothing wrong with checking and 'nixing' those 'was's that are weakening the prose.
Not counting the referential use of "was," you used some form of the verb "to be" three times in that sentence alone, and the only one I would even consider nixing is "that
are weakening": you could say "that weaken," but even that is a mere stylistic quibble. Otherwise it works fine.
The reason it works just fine to use "to be" all over the place in English prose is because "to be" is an irregular verb, so it doesn't look or sound repetitive:
is,
's, and
are provide variation simply because they look and sound different. By contrast, if you used versions of the verb "to talk" three times in a sentence, it would sound ridiculous because the verb is regular: "I talked to him about talking to her, and he said they already talked..."
But I agree that there are three circumstances in which nixing "to be" is clearly desirable:
(1) when there is a more vivid verb you could use in its place that works better for the story: "She is beautiful"--why not "She dazzles every man she meets," or something to that effect?
(2) when you're using it to create a passive-voice sentence, and the sentence would work better in the active voice: "The jewels were eaten by Seigfried and Roy's tigers" --> "Seigfried and Roy's tigers ate the jewels"
(3) when it's used as what I think of as "verbal throat-clearing," adding meaningless words to get a sentence or clause started: "
There is a reason I called you here today, and
it is because..." --> "The reason I called you here today is that [or is because]..."
