EDIT: This is a fast evolving situation. Under the current circumstances I suggest anyone planning to come to Europe just cancel or postpone.
A Schengen visa normally allows one to enter any Schengen country.
There is no obligation to enter the Schengen area through the country that issued your visa.
So entering via France (or any other country) is not an issue.
It is pretty common even.
The rule that you must apply to the consulate of the country that is your main destination exists to spread the workload, and to counter visa shopping.
To enforce that rule the immigration officer stamping you in may want to see hotel and flight reservations proving that indeed you plan to follow the itinerary on your Schengen Visa application.
Arriving at the border with evidence suggesting that your plans are very different from those stated in your application will raise red flags, and may lead to a refusal.
This under normal circumstances.
However we are no longer under normal circumstances.
Deciding to no longer visit Italy is completely reasonable in light of the current situation.
So I would guess that cutting Italy out of your plans is not going to raise a red flag.
You should however inquire with the French consulate and the French border police (email@example.com).
One last thing:
The way things are currently progressing all of Europe will be where Italy is now in about 10 days (and so might your home country).
You might want to completely postpone your trip.