After being demilitarized in 2005, Sweden re-introduced permanent troops to Gotland in 2016, following Russia’s annexation of Ukraine’s Crimean Peninsula in 2014. Sweden also became NATO’s newest member in March — meaning it is covered by the alliance’s Article 5 guarantee that all other members come to each other’s defense if they are attacked.
You may be forgetting that Kaliningrad is another Russian harbor in close proximity. Don’t know if there’s any credence to assertion that Gotland is in danger, but just saying.