sick,
While I agree that one needs to be more careful about betting favs than dogs, the notion that you are putting more at risk is fallacious...to illustrate, consider the following two betting propositions:
A) bet $900 on a line of -900
B) bet $500 on an even money line
Assume both are fair propositions ie. that A) has a 90% chance of success and B) has a 50% chance. I say you are taking a greater risk if you choose B) than A), despite A) having the larger bet amount.
A well-known formula for the binomial distribution says that if you have n trials with a probability p of success, then the standard deviation is given by sqrt(n*p*(1-p))
So if you place the bet 100 times, the standard deviation of proposition A) is sqrt(100*.9*.1) = sqrt(9) = 3
And for B) the s.d. is sqrt(100*.5*.5) = sqrt (25) = 5
This means that after 100 plays, your 95% confidence limits for propostion A) (which is plus or minus 2 s.d.'s from the mean) is 84 to 96 wins, which translates to plus or minus $6,000. While for B) these are 40 to 60 wins, or plus or minus $10,000.
Therefore, you are taking a 1.667 times greater risk with B) than with A)
Another way to look at it is to see what happens if you have bad luck to the tune of a 1000:1 shot coming in against you in your first sequence of bets. With A) this translates to 3 losses in a row which will cost you 3 bets or $2,700. With B) this would be about 10 losses in a row (a 1024:1 shot which is not exactly 1000, but close enough) which would cost you $5,000
Of course if your chance of winning is not really 90% in the first case, the numbers change dramatically, so the idea of being careful with favs is still a valid one.