I like several bets, I think it's one of the biggest advantages of roulette over other chance games, e.g. dice games. I disagree that making one bet is more profitable, even in your example:
Let's imagine that you decide to play at odds and bet $1 on every even number and $2 on every odd number. Total in the amount of your costs is $54. If you get an even number, your winnings will be $35 (1*35). If you roll odd, the payout will be $70 (2*35). If it comes up zero, you lose all of that set $54.
In such a case is you get an even number you win $35, but you should substract $35 from your winnings for $2 per each odd number that you've lost in this round, means you lose 0 and win 0. If you roll odd - you get $70-$18=$52 (for $1 per each even number during this round). So you either gain and lose 0, or win $52, that's exactly a win-win situation. And the probability of rolling zero is 1/36, which is much less than rolling either even or odd number (which is exactly 1/2).
If you follow the strategy of one bet, the results of the next round of European roulette will look very different for you. Let's imagine you only place one bet $35 on even numbers only. If your bet wins and it falls even, you win $70. If the bet loses, you lose $35. Your costs in this case are lower ($35 vs. $54), and the chance of winning in each of the two cases is exactly the same.
And I disagree here, placing only one bet chances of losing jump from 1/36 to 1/2, even though the amount of your losses is less in this case eventually you'll lose more with this strategy.