When we pledge margin is provided by the clearing corporation and not the broker. Broker charges interest only if there is a shortfall in client account which can happen in both option selling or buying if there is a M2M lose. As you may know M2M in option selling can quickly go much above the premium collected if market moves against you.
Any expiry option is allowed.
Besides those who denounce option buying never operated for meaningful amount of time within the profitable contours of option buying.