doyle is talking about suited connectors like 76s not 76o. While being suited usually only gives another percent of equity vs someone's range, it completely changes how profitable they can be. The reason for this is the combo draws we can get when playing them. For instance, had you had 7d6d, you would have 15 outs to win the hand, and be a significant favorite on the flop which is completely different than the current 6 out scenario.

I don't like raising preflop, simply because i do want to see a flop with alot of people when i play a hand like 76s, however, im also willing to fold if i hit a 7 high flop. The reason for the limp is to get the right odds to play it in the first place. The chances of hitting a straight or flush draw is about the same as hitting a set with a pocket pair. So, we would like alot of people in the pot to get the right pot odds/implied odds.

i hate raising preflop, but i play as a tagg player. If your style is geared more towards loose aggressive play, then the arguement goes along with the fact that limpers usually don't have a strong enough hand to raise, by raising you gain control of the pot, and if called, you have a chance to win the pot on the flop with a cbet since most flops miss a single opponent. Of course, if we are aware that someone is limping hands as strong as JJ or if we see limps from utg we should be wary when doing this kind of play. Like i said though, i hate raising this pre.