A quick German victory required getting around French defences, and the route through Belgium threatened permanent occupation of strategically important territory. A hypothetical Channel attack might have been easier for Britain to tolerate. German victory could leave Britain without continental allies and dependent on German friendship for its security. That dependence would require trusting Wilhelm II's government.
Notable Point · 1:47:23-1:48:52
Neutrality risked making Britain dependent on Germany
A German victory through Belgium could leave Britain isolated and reliant on Wilhelm II's goodwill in a German-dominated Europe.