It is disappointing to see people only thinking of themselves, when it comes to the idea of taxation. Destroying gil is an incredibly valuable feature, and serves the poorer players in very important ways - materia costs are lost, the cost of crafting gear sets is less, inflation in general is just plain less, making it easier to actually buy what you need to support your progress in becoming an earner, as opposed to someone with no means of generating gil.
Using the example Terrini provides, of your casual non-crafting player struggling to get a cottage for themselves, I'd like to call attention to two things: Firstly, on Brynhildr, 5% of the most expensive small lot size would work out to be 125,000 gil a month. That is easily obtainable by anyone who has been 50 for a month or two.
Secondly, please consider the example of Terrini in this way also - if Ter's server had a gil devouring housing rent engine chewing away at the savings of the mansion-owning master crafters, the server would have less total wealth in circulation, which would mean the price in pure gil of entry into crafting and gathering careers would be that much less, and more quickly reachable through gil generated as opposed to gil taken from other players. I shouldn't have to explain the importance of the distinction between those two income sources, and how they relate to new players and the barrier of entry they face when growing towards crafting for profit.
Please! Consider the broader advantages of having gil destroyed on a monthly basis. We associate the word "tax" with feeding some greedy fatcat money-for-nothing, but that really isn't how gil destruction works at all.
Think of it like this - Monsigneur Mansion has 1,000,000 gil. Cody Cottage has 100,000 gil. A tax of ten percent kicks in, and the His Highness now has 900,000 gil, and Cody Cottage has 90,000 gil. Who lost more? Mr. Mansion. Who'll have an easier time making up for the loss? Mr. Cottage. This form of gil destruction is the best and most useful means of reducing the distance between the haves and the have-nots because it almost exclusively targets the haves - homeowners.