The issues you mention above, is why, a gate on an easements are normally not allowed in residential areas, as it an excessive burden to the dominant title holders, now and into the future.
Why do the servient title holders want the gate, locks and insurance? most likely to piss you off and to stop you using the land, which will have no weight in court.
Just remember, that you or the previous owner, most likely paid a fee to the servient title holder (or previous holder) to use that piece of land, and now after the fee has been spent, they want to decrease your enjoyment of the easement.
Write a letter, stating, that the proposal is an burden to your enjoyment of the easement (now and into the future etc) and reasonable force will be used to remove any gates and locks. Also get other users to right the same letter and send it to them.
if you end up cutting locks etc, and they call the police, the police will tell you/them its a civil matter and they wont do a thing as, you have a legal right to access that part of the land.
And finally, if you do let them put the gates up etc, good luck getting them removed in the future.