Is "Thus" stilted at the beginning of a sentence?

That use of "thus" (ainsi) in French ties in with the entire "explication de texte" stylistic frame that includes such gems as ainsi, donc, par ailleurs, par conséquent, finalement, en conclusion, among others.

You make your main statement and then support it by a series of secondary statements where the paragraphs will often start with an adverb which marks the next part of the argument. The "thus" will often mark an outcome or result at the end of paragraph's argument. Or even at the end of the essay.

For your sample sentence, I'd prefer: In short, and I would also get rid of the "We can say" ( a royal we) which is another turn of phrase used in French to avoid saying "I think" or "In my opinion". In English, it's OK for students to give their opinions in the first person. Although "Therefore" can be used to show an outcome, it seems to me that this:

• Thus, we can say that the toppling of statues by angry mobs is an attack on democracy.

is more punchy expressed like this:

• In my opinion, the toppling of statues by angry mobs is, in short, an attack on democracy. OR
• The toppling of statues by angry mobs seems, in short, to be an outright attack on democracy.

The word therefore in English does in fact show an outcome contrasted with what precedes it. I don't see that much difference with thus, but probably would not use either here, as explained.

[Please note: I call them gems because they really are. They can really help one learn to get a grip on the French essay writing style.]

in short - Collins Dictionary

PHRASE You use in short when you have been giving a lot of details and you want to give a conclusion or summary.

Ainsi, nous pouvons dire....

A minor point: In English, we do often put thus, therefore and other adverbs of this type, elsewhere in the sentence: It is, therefore, reasonable to argue etc. It is, thus, admissible to argue... That's a style trick that is useful to know.