So... would they start shooting if hundreds of Russian civilians blocked the entrances of military bases, protesting the troop movement as an alleged crack down on their rioting friends in Tallinn? This, as "polite people" take over the part of Estonia Russia intends to keep.
Think then of what next. If the answer is no, then their response would at least be seriously slowed, letting Russia effectively take out provinces in the east. If the answer is yes, then Russia has their justification for full scale military action, tanks and all. And think of the images, all over the world media. Dead Russian protesters shot by the Estonian military, this after a history of discrimination against their Russian population in modern times. Russia would then easily claim that their military action was caused by this. Their claim may get acceptance, or not (likely not, in the long run the west has much more power in the information sphere, only think back to 888) but it would be too late. The situation would be sufficiently messy, the EU and NATO response necessarily slow, and the entire thing would be presented as a fait accompli.
Consider how long it took for the EU and NATO to finally act in response to Russia's actions in Ukraine. Inertia is a powerful thing. Honestly, in retrospect, Putin's actions in Ukraine may have been the best thing the Baltics could hope for. Now they've been justified in their fears, and have serious protection from the west. But before that?