Should there be a max buy-in for a "friendly" .10/.20 game?

That's kind of my argument.

First of all, if I have accumulated chips from playing a pretty solid game and have built my stack to $30-40 in a short-handed game, or $50-$80 in a full game (remember, this is .10/.20), why should I let a crap shooting player (i.e. loves the action and loves to beat the odds) come in for the same amount and eventually beat the odds and take my hard-earned stack from me?

PS this has happened before, hence the new rule.

Second, raising the buy-in to this amount, changes the texture of the game and makes it a more serious game, at least for me it does.