There is also the other side to consider. By not boycotting or sanctioning an aggressor you're supporting their efforts by supplying material or funds through trade.

When a government has a proven record of bullying or annexing their neighbors I think boycotting is the least one can do. And collective sanctions among allies is a reasonable next step where diplomacy fails.

In the case of Russia sanctions weren't even enough to stop them after they annexed Crimea. No one wants to continuously cave into a bully then pretend it's "peace in our time".