Exactly, developing players for the national team is important but so is growing soccer culture in this country. This great sport of ours is about more than just being the best or even being good it's about bringing the community together. As for second teams being in the league I've always been against it for multiple reasons. 1st it's bad for the league's image, it would set it clearly in minor league territory. 2nd, I don't think they would be anywhere near competitive, VWC2 and TFC2 were USL bottom feeders this year and rumor is many USL teams have total payrolls short of 700k a year. 3rd, I believe it would hurt other teams, what casual fans wants to see their local team play a 2nd team. 4th having independent teams in MLS markets would push competition more, while second teams in the league would prop up the MLS teams monopoly in the market.
However I believe at the youth level MLS teams and future CPL teams should compete together. For example I'd like to see Ontario CPL teams to put senior academy sides in L1O like TFC3 is. I'd also like to see the impact's oldest academy team along with any CPL teams in Quebec(or Ottawa) to play in the PLSQ. I'd like to see similar things happen around the country with regional youth focused senior leagues(like L1O) being home to smaller market senior teams and pro teams 2nd/academy teams.