It's a shame that most likely this can't be a coordinated total shutdown and no doubt FR will pull out all the stops to minimize disruption.
However provided the planned strikes actually go ahead and result in a significant and visible number of canceled flights this action will have a massive psychological impact for customers, media and the markets.
For the markets it will be a clear demonstration that FR have lost their iron grip on IR. That any significant number of crews are willing to actually walk out sends a very strong message.
The dispute has already caught the attention of various authorities around Europe, so any retaliation against striking crews will attract intense regulatory & media interest and possible legal actions. Sneaky tactics like failing SIM are not going to fly under such scrutiny.
Striking FR crews have commitments from worldwide unions to provide legal support and funding if required. This support WILL be forthcoming if needed because the outcome of this dispute maters to the whole industry.
FR will have a difficult time turning the public against striking crews for any disruption - due to the shambolic handling of the previous cancellations, the public will blame FR regardless.
TLDR;
Anyone who can should not be afraid to join the strikes because practical and legal support is in place that goes well beyond mere platitudes.
You have far, far more to loose by failing to follow this through.