If it's not now, it will be soon. One day you'll notice your tire needs air. But you won't be able to add any because the slime sealed the valve. So then you'll be stuck with a semi inflated tire. You'll get frustrated and angry that you can't fill your tire. You'll have a drink to calm down, then another, then another. You'll be too tired and drunk to ride so you'll sit on the couch and watch TV. Every time you think of your tire, you'll get pissed off and have another drink and flop on the couch. You'll stop riding, get fat and, die on your couch.
Don't use slime, it will kill you.