It's not about being hostile/combative or you being too open; it's business.

When a company (or person) asks you to sign a contract, it's an offer presented and written entirely for their benefit. There's no reason at all to attempt to make it "fair" - nor should they. It's your job to take care of your interests and to walk away or push back. Their only interest in trying to make the contract amicable is to seal the deal quickly and/or to not burn bridges.

This is true with everything. If you want to buy a house, the offer you make should be about getting the most for your money. Mentally, you may want to be "decent" with your offer, but that's really just about trying to close the deal quickly before another offer is presented to the seller.