For security reasons I consider any project employing the referral system marketing's strategy to promote their already launch coin as a MLM Ponzi scheme. Now if the project is still in the development phase and engage in referral marketing to attract investors for crowdfunding such strategy is understandable and acceptable.

If your already launch coin can't survive without referral marketing that's the coin can't sell itself, it's not worth investing in and Investors should stay away from such coins as they're bond to fail.